1. 1trnh o toccGIO TRNHAN TON H THNG THNG TIN 2. 2MC LC MC TRANG1. LI TA ........................................................................................................... 32. GII THIU V M UN MN HC ................................................................ 53. S QUAN H THEO TRNH T HC NGH ............................................. 64.CC HNH THC HC TP CHNH TRONG M UN/MN HC ................... 85. BI 1: PHN TCH CC NGUYN NHN DN N MT AN TON TRONGH THNG THNG TIN ................................................................................... 96.BI 2: LU TR H THNG THNG TIN TRN CC THIT B LU TR .... 177.BI 3: VIRUS TIN HC V CCH PHNG CHNG ......................................... 498.BI 4: MT S BIN PHP AN TON CHO CC H THNG MY TNH ...... 589.BI 5: MT S PHNG THC M HO V GII M D LIU ................... 6810.BI 6: XY DNG K HOCH BO V H THNG THNG TIN TRNMY TNH ........................................................................................................ 8011.TI LIU THAM KHO ..................................................................................... 100 3. 3BI 1Tn bi: PHN TCH CC NGUYN NHN DN N MT AN TON TRONG H THNG THNG TINGii thiu :Khi ni n an ton thng tin (ATTT), iu u tin ngi ta thng ngh n l xy dng tng la (Firewall) hoc mt ci g tng t ngn chn cc cuc tn cng v xm nhp bt hp php. Cch tip cn nh vy khng hon ton ng v bn cht ATTT khng n thun ch l s dng mt s cng c hoc mt vi gii php no m m bo ATTT cho mt h thng cn c mt ci nhn tng qut v khoa hc hn.Mc tiu thc hin:- Xc nh tt c nhng nguyn nhn dn n d liu trn my tnh b mt- Phn tch nhng nguyn nhn a n vic r r thng tinNi dung chnh:1.1 Vai tr quan trng ca thng tin trong mt n v.Vy an ton thng tin l g?Khng th m bo an ton 100%, nhng ta c th gim bt cc ri ro khng mong mun di tc ng t mi pha ca cc lnh vc hot ng kinh t x hi . Khi cc t chc, n v tin hnh nh gi nhng ri ro v cn nhc k nhng bin php i ph v ATTT, h lun lun i n kt lun: nhng gii php cng ngh (k thut) n l khng th cung cp s an ton. Nhng sn phm Anti-virus, Firewalls v cc cng c khc khng th cung cp s an ton cn thit cho hu ht cc t chc. ATTT l mt mt xch lin kt hai yu t: yu t cng ngh v yu t con ngi.1. Yu t cng ngh: bao gm nhng sn phm nh Firewall, phn mm phng chng virus, gii php mt m, sn phm mng, h iu hnh v nhng ng dng nh: trnh duyt Internet v phn mm nhn Email t my trm.2. Yu t con ngi: L nhng ngi s dng my tnh, nhng ngi lm vic vi thng tin v s dng my tnh trong cng vic ca mnh.Hai yu t trn c lin kt li thng qua cc chnh sch v ATTT.Theo ISO 17799, An Ton Thng Tin l kh nng bo v i vi mi trng thng tin kinh t x hi, m bo cho vic hnh thnh, s dng v pht trin v li ch ca mi cng dn, mi t chc v ca quc gia. Thng qua cc chnh sch v ATTT , lnh o th hin ch v nng lc ca mnh trong vic qun l h thng thng tin. ATTT c xy dng trn nn tng mt h thng cc chnh sch, quy tc, quy trnh v cc gii php k thut nhm mc ch m bo an ton ti nguyn thng tin m t chc s hu cng nh cc ti nguyn thng tin ca cc i tc, cc khch hng trong mt mi trng thng tin ton cu. Nh vy , vi v tr quan trng ca mnh , c th khng nh vn ATTT phi bt u t cc chnh sch trong con ngi l mt xch quan trng nht. 4. 4Con ngi khu yu nht trong ton b qu trnh m bo an ton thng tin . Hu nh phn ln cc phng thc tn cng c hacker s dng l khai thc cc im yu ca h thng thng tin v a phn cc im yu rt tic li do con ngi to ra. Vic nhn thc km v khng tun th cc chnh sch v ATTT l nguyn nhn chnh gy ra tnh trng trn. n c l vn s dng mt khu c quy nh rt r trong cc chnh sch v ATTT song vic tun th cc quy nh li khng c thc hin cht ch. Vic t mt mt khu km cht lng, khng thay i mt khu nh k, qun l mt khu lng lo l nhng khuPhng php nh gi cht lng h thng ATTTC l khng mt v lnh o no dm khng nh ni b cng ty l thc s an ton v tin cy. Trong bi cnh nn kinh t th trng nh hin nay, s canh tranh din ra gay gt thm ch gia cc nhn vin trong ni b cng ty: tranh dnh khch hng , mc ch thng tin hoc cc mc ch khng lnh mnh khc. mt s t chc, li dng s lng lo trong qun l v ATTT, nhn vin c nhng hnh vi bt lng nh ly cp thng tin mt, chim ot ti khon khch hng , n cp tin thng qua h thng tn dng Theo thng k, khong 70% cc ri ro v ATTT l xut pht t ni b trong t chc. Mt trong nhng cu hi lun c t ra trc cc nh lnh o v cc nh qun tr thng tin l: H thng thng tin ca t chc an ton n mc no? Cu hi ny l mi quan tm ln nht v cng l vn nhy cm nht trong cc khu qun l h thng thng tin.Tr li cu hi ny tht khng n gin nhng khng phi l khng c cu tr li. gii p vn trn, ch yu da vo hai phng php nh gi ATTT nh sau: + Phng php nh gi theo cht lng ATTT ca h thng bng cch cho im.V d: h thng t 60/100 im hoc 60%+ Phng php nh gi theo s lng thit b - cng ngh bo mt.Trong thc t , phng php nh gi theo cht lng l phng php duy nht nh gi mc an ton ca cc ti nguyn trong h thng thng tin. Vit Nam, vic nh gi ATTT theo cht lng l hon ton mi. Ngi ta d ng nhn vic trang b mt cng c ATTT nh (Firewall, Anti-virus) l m bo c ATTT cho h thng. Cht lng ATTT phi c nh gi trn ton b cc yu t m bo tnh an ton cho h thng t t chc, con ngi, an ninh vt l, qun l ti nguyn n vic s dng cc cng c k thut. Ni cch khc, cht lng ATTT c nh gi trn c s thc thi cc chnh sch v ATTT trong h thng. Cc chnh sch ny c chun ho v c cng nhn l cc tiu chun v ATTT p dng trn phm vi ton th gii.Phng php nh gi theo s lng khng c s dng.Tiu chun nh gi v cht lng ATTT.Vic nh gi mc ATTT ca cc t chc thng c tin hnh theo kinh nghim v da trn cc quy nh mang tnh cm tnh , cc b ca t chc m khng tnh n cc tiu chun c th gii cng nhn . Vi nm trc y, Vin Tiu chun ca Anh (BSI) cng vi mt s t chc thng mi khc nh Shell, National Westminster Bank, Midland Bank nghin cu v xut mt tiu chun v ATTT. n nm 1995, tiu chun ny c cng nhn l tiu chun quc gia v qun l ATTT - BS7799. Tiu chun ny c lp vi m hnh hot ng ca cc cng ty. Lnh o cng ty, cc CSO/CIO da trn c s cc tiu chun ny thit lp cc chnh sch ATTT cho n v mnh. Ngay sau khi ra i, BS7799 c s dng 27 nc bao gm cc nc thuc khi lin hip Anh cng 5. 5nh mt s quc gia khc nh Thy S, H Lan... n nm 2000, T chc tiu chun th gii ISO trn c s BS7799 xy dng tiu chun ISO 17799 v tiu chun ny tr thnh tiu chun quc t v qun l cht lng ATTT (ISO/IEC 17799). Tnh n thng 2/2005 c khong hn 1000 t chc nhn chng ch ISO 17799 trong c Hitachi, Nokia,Nhng phn c bn ca ISO 17799:1. Chnh sch chung 2. An ninh nhn s (Personel Security) 3. Xc nh, phn cp v qun l ti nguyn (Asset Identification, Classification & Control). 4. An ninh vt l (Physical Security). 5. An ninh t chc (Security Organization). 6. Qun tr IT v mng (IT operations and network management). 7. Qun l truy cp v cc phng php (Access control & methods). 8. Pht trin HT v bo tr (System development & maintenance). 9. Tnh lin tc trong kinh doanh v k hoch phc hi sau s c (Bussiness Continuty & Disaster Recovery Planning) 10. Ph hp h thng vi cc yu t v lut php, o c (Low, Inestigation and Ethics).Hnh 1.1 Nhng phn c bn ca ISO 17799Chnh sch v an ton thng tin c t chc theo m hnh kim t thp.Cch t chc ny gip cho cc nh lnh o qun l cht lng an ton thng tin mt cch khoa hc v hiu qu. Trn nh kim t thp m t cc chnh sch c p dng trong t chc .Ti sao ta phi thit lp chnh sch ny ? Phm vi v i tng tc ng ca chnh sch? . Khng c mt chnh sch p dng chung cho mi n v. Trong mt t chc c nhiu b phn , tng b phn li c chc nng nhim v khc nhau, tnh cht v cch t chc thng tin cng khc nhau .B phn kinh doanh c m hnh thit k h thng ring vi c s d liu mang c th kinh doanh , b phn sn xut ,b phn nghin cu cng c cu trc h thng v c s d liu ca ring mnh .Trnh nhn thc v an ton thng tin cng rt chnh lch . Chnh v vy khi thit lp cc chnh sch ,nh qun l cn xc nh r mc ch ca chnh sch c thit lp , i tng thc thi , phm vi tc ngLp th hai trn m hnh m t cc quy tc ,quy nh thc thi cc chnh sch . thc hin cc chnh sch ta phi lm g ? H thng cc quy tc ATTT c th hin trn 10 lnh vc ln bao hm cc quy nh t t chc , con ngi , an ninh vt l n cc cng c k thut an ton thng tin .Cc quy tc c xy dng trn m hnh IT chun ca t chc v th hin 6. 6c tnh c th ca t chc .Thng qua vic thc thi cc quy tc , c th nh gi cht lng an ton thng tin ca mt t chc thng qua kim ton (Audit) .Lp th ba l lp cui cng ca m hnh . y l cc quy trnh , cc gii php h tr thc thi cc quy tc , quy nh trn.N tr li cho cu hi lm nh th no thc thi cc quy nh trn ? Cc nh qun tr an ton thng tin (CSO) cng cc qun tr IT thit lp cc quy trnh ny v ph bin n mi nhn vin trong t chc ,v d Quy trnh thay i mt khu,Quy trnh ci t cc chng trnh dit virut ,chng cc chng trnh c hi v.v.Cc quy trnh ny c th lin quan n nhiu chnh sch v i tng s dng khc nhau.Vic p dng ISO 17799 em li li ch g cho t chc?Vic p dng cc tiu chun v ATTT theo ISO 17799 lm tng nhn thc cho i ng cn b nhn vin v ATTT. Xy dng mt mi trng an ton, c kh nng min dch trc cc ri ro, gim thiu cc nguy c do con ngi gy ra. Tiu chun ISO 17799 ra nhng nguyn tc chung trong qu trnh thit k , xy dng h thng thng tin mt cch khoa hc, gip cho vic qun l h thng tr nn sng sa, an ton, minh bch hn. Chng ta xy dng mt bc tng ngi an ton (Secure People Wall) trong t chc. Mt mi trng thng tin an ton, trong sch s c tc ng khng nh n vic gim thiu chi ph vt cht u t cho ATTT vn d rt tn km. V lu di, vic nhn c chng ch ISO 17799 l mt li khng nh thuyt phc vi cc i tc, cc khch hng v mt mi trng thng tin an ton v trong sch . To iu kin thun li cho s hi nhp mt mi trng thng tin lnh1.1 Vn o to ngun nhn lcTheo IDG vo khong nm 2006 s bng n mt ngh mi trong lnh vc IT ngh an ton thng tin.Chc danh CSO (Chief Security Officer) tr nn quen thuc trong lnh vc IT. Cp nht v nng cao kin thc v ATTT v nhn thc v vai tr ca n trong h thng IT l mt iu rt quan trng v cp bch v xt cho cng hnh ng ca con ngi l yu t quyt nh . Mc d ATTT c bit n rng ri nhng yu t con ngi thng t c cc t chc quan tm n. i vi nhng nh qun tr, h cn mt chnh sch an ton v mt chng trnh nhn thc cng nh nh gi cht lng v ATTT nhng tic rng hin nay cha c nhiu gii php thc s quan tm vo vn lm sao tng cng s vng chc cho mi lin kt vn d rt yu t ny trong mt xch ATTTHin nay, mt s doanh nghip ti Vit Nam c s chuyn bin tch cc trong vn nhn thc v ATTT. H sn sng u t ngn sch o to ngun nhn lc nhm to nn tng vng chc v nhn thc v kin thc ATTT cho i ng nhn vin ca doanh nghip. in hnh l nh: S Khoa hc v Cng ngh ng Nai, Cng ty Bo him Bo Minh, Fujitsu Vietnam, Ngn hng Chu ...Bn cnh vn cn nhiu doanh nghip nht l cc doanh nghip va v nh vn cha tip cn v hiu ht tm quan trng ca vic thit lp cc chnh sch v ATTT v qun l tiu chun cht lng ATTT theo ISO 17799 thc s vn cn xa l v mi m i vi h. 1.2 Phn tch nhng nguyn nhn a n thng tin trn a b mt 7. 7-RAID controller b hng.( Redundant Array of Independent Disks) -Ngi dng v hoc khng lu thay a mi khi a b h,gy ra s h hng ca a khc trong cng mt RAID. -D liu RAID registry trong b nh b hng. -Tng v tt in p t ngt, thm ha t nhin. -Li do ngi s dng, v tnh xa thng tin hoc li phn mm ca a cng. -Ngi s dng reconfigure dung lng a cng sai. -Virus tn cng hoc ngi s dng v tnh nh dng sai mt a cng trong h thng RAID.RAID l ch vit tt ca Redundant Array of Independent Disks. Ban u, RAID c s dng nh mt gii php phng h v n cho php ghi d liu ln nhiu a cng cng lc. V sau, RAID c nhiu bin th cho php khng ch m bo an ton d liu m cn gip gia tng ng k tc truy xut d liu t a cng. Tuy nhin vic mt d liu t RAID khng phi l chuyn khng c, v ngi s dng thng cm thy ch quan v RAID nn thiu s sao lu d liu cn thit.Cc loi RAID: RAID 0: Cn c gi l "Striped Volume", n c s dng gia tng s truy cp d liu. Trong cu hnh RAID 0 ny n c th h tr t 2 disks cho n 32 physical disks, d liu c chia u ra trn cc disks, v n lm vic nh l mt logical khi (Volume). Mc d n c gi l RAID (Redundancy Array of Inexpesive Disk), nhng tht s trong cu hnh ny n khng c "Redundancy". Vi cu hnh RAID ny, nu mt trong hai disk ca khi RAID ny rt th s truy cp d liu vo khi ny s b mt ht.RAID 1: Cu hnh RAID ny cn c gi l cu hnh "Khi Phn Chiu" (Mirrored Volume), trong cu hnh ny d liu c mirrored gia hai physical disks cho mc ch redundancy. Vi RAID 1 tt c nhng d liu c vit v volume th nht trong khi mirrored th n s c vit v volume th hai trong khi ny bi fault tolerant driver ftdisk.sys. D liu v vy c m bo an ton hn Raid 0.RAID 1+0: L s kt hp ca Raid 0 v Raid 1 vi s hin din ca Fault Tolerance a ra mt h thng hon ho c u im ca c hai loi Raid,s nhanh nhy ca Raid 0 v s an ton ca Raid 1.Tuy nhin chi ph cho mt h thng ny kh t v phi cn t nht 4 a cng c th thit lp.RAID 5: RAID 5 thng c bit nh l "Stripe set with parity". Trong cu hnh RAID ny, n s dng t nht l 3 v nhiu nht l 32 physical disks, khng ch ring d liu c phn phi u trn cc disk m nhng thng tin lin kt cng c phn phi trn cc disks, chc chn rng d liu s c cu thnh li nu mt trong nhng disk c lp b rt. Ni ng hn l nu bt k disk no trong khi ny b rt th bn c th thay i mt disk mi v n s t ng cu hnh li (Rebuild) tt c nhng d liu b mt.Cc loi RAID khc: Ngoi cc loi c cp trn, bn cn c th bt gp nhiu loi RAID khc nhng chng khng c s dng rng ri m ch gii hn trong cc h thng my tnh phc v mc ch ring, c th k nh: Level 2 (Error-Correcting Coding), Level 3 (Bit-Interleaved Parity), Level 4 (Dedicated Parity Drive), Level 6 (Independent Data Disks with Double Parity), Level 10 (Stripe of Mirrors, ngc li vi RAID 0+1), Level 7 (thng hiu ca tp on Storage Computer, cho php thm b m cho RAID 3 v 4), RAID S (pht minh ca tp on EMC v c s dng trong cc h thng lu tr Symmetrix ca h). Bn cnh cn mt s bin th khc, v d nh Intel Matrix Storage cho php chy kiu RAID 0+1 vi ch 2 cng hoc RAID 1.5 ca DFI trn cc h BMC 865, 875. Chng tuy c nhiu im khc bit nhng a phn u l bn ci tin ca cc phng thc RAID truyn thng.1.3 Phn tch nhng nguyn nhn a n r r thng tin trn my tnh 8. 8R r thng tin trong doanh nghip qua th nh:Thng thng, mi ngi c th dng nhng thit b kiu ny t do trong gi lm vic m khng cn s cho php ca cp trn. Th nh c nhn vin mang i khp phng v cm vo cng USB sao chp bi ht c sn trong my tnh ca ngi khc.Tuy nhin, s lng lo ny s tip tay cho bt c ai cng c th lu ton b thng tin trn my tnh no vo trong th nh dung lng ln mt cch c ch ht sc nhanh chng.R rng, trong khi nhiu hng tiu tn c ni tin bo v mnh thot khi nguy c t virus, spyware, spam..., th h li qun li cnh bo mun thu ca cc chuyn gia bo mt rng him ha ln nht bao gi cng nm chnh bn trong mi cng ty.Mt s hng thc hin nhiu bin php ngn cn vic sao chp d liu t my tnh vo th nh v my nghe nhc, nhng cm dng nhng thit b ny l v l v s khng th thc hin c trn thc t. Do , cc cng ty cn trang b nhng cng c, ng dng tinh vi c th ghi li hot ng ca ngi trong mng ni b trnh tht thot d liu, r r thng tin hoc nhim virusR r thng tin trong doanh nghip qua my tnh xch tay:Trong nhiu trng hp, nhn vin mang thng tin ca cng ty ra khi vn phng bng chic laptop. Tuy nhin, h khng bo v s an ton cho chng v t ra ngi ngn khi dng cc c ch m ha nh ci password cho my v cc tp tin. Alan Paller, Gim c Hc vin SANS chuyn nghin cu vn bo mt my tnh, gii thch l do l nu h qun mt khu th s khng m c tp tin v cc thao tc ny c v lm chm cng vic ca h.iu ny khin cc nh sn xut my tnh lu tm v bt u tch hp c ch m ha vo sn phm. V d nh h iu hnh Windows Vista ca Microsoft s gip ngi s dng d dng m ha d liu ca mnh hn.Cc cng ty c lng ln nhn vin di ng cng bt u quan tm n iu ny. V d nh hng t vn ti chnh Ernst & Young vi 30.000 my tnh xch tay phc v cho cng ty ang m ha tt c ni dung trn my sau v thng tin v 243.000 khch hng ca h cha trong mt chic laptop b nh cp, bao gm tn, a ch, thng tin th tn dng.1.4 Mt s bin php khc phc.Cc chuyn gia a ra li khuyn vi cc bc sau: 1. Phi kim sot d liu Chc chn bn khng th no kim sot c thng tin nhy cm hay thng tin bn quyn trn mng nu ngay c v tr ca chng nm u bn cng khng bit. D liu nhy cm ca mt t chc thng c phn phi rng ri qua mng ni b. D liu quan trng thng khng ch nm trong c s d liu (CSDL) m c khi c trong th in t, my tnh c nhn v i khi ng vai tr nh kiu i tng d liu trong cng Web. Thng tin nhy cm cng c nhiu kiu khc nhau, nh m s th tn dng, m s bo mt x hi (CMT, th sinh vin). Cc b mt thng mi c th c tm thy trong nhiu loi file, vn bn khc nhau theo kiu thng tin lin h khch hng, hp ng, chi tit k thut pht trin sn phm. Trin khai quy nh kim sot cho tt c cc loi d liu thng khng mang li hiu qu v khng thc t. Thay vo , hy phn loi tng lp d liu v chn ra quy nh kim sot ph hp nht cho mi loi. Bn cng c th s dng mt s cng c r sot mng t ng v xc nh v tr d liu nhy cm. Nhiu hng cung cp cc loi cng c ny nh Reconnex, Tablus, Websense. S lng sn phm ca cc hng ngy cng phong ph. Nhiu trong s c th phn tch d liu thnh nhiu loi khc nhau, da trn quy nh do cng ty t ra. 2. Gim st ni dung di ng Khi cc cng ty s dng Website trong giao dch thng mi v lin kt vi nhiu mng 9. 9thuc v i tc, nh cung cp hay khch hng th vn sng cn l phi theo di c ci g ang din ra, ang tri ni qua cc mng. Gim st ni dung l phn c s ct li trong chin lc bo v d liu ca nhiu cng ty. Vi qu nhiu im ra mng cho d liu, iu quan trng nht l phi gim st c lu lng mng. Tt c cc hng sn xut nh Vericept Corp., Vontu Inc., Oakley Networks Inc., Reconnex v Websense u bn mt lot sn phm c chc nng kim tra, r sot e-mail, trnh tin nhn tc thi (Instant Messaging), h thng chia s file peer-to-peer, qu trnh post Web v c cc website FTP nhm pht hin v tm kim hot ng xm phm d liu hay vi phm quy tc t ra trong cng ty. Cc cng c ny c t gn cng vo mng v c thit k a ra cnh bo khi pht hin gi d liu ng ng. Nhiu sn phm c th c dng thc p cc hot ng nh loi b hay m ho d liu khi d liu c truyn ra ngoi. V d, mt trong s l cc cng c lc ni dung, cho php bn thy c tt c nhng g ang n hoc ang ra ngoi mng. Nh Bowers ca cng ty hng u Wyeth nhn xt: Chng ti gim st c tt c cc cng v tt c giao thc truyn ti ni dung khi hng ny trin khai cng c lc ni dung. 3. Hy mt n c s d liu c cha nhng thng tin qu bu ca cng ty ng dng li vic bit ai ang truy cp c s d liu. Bn cn cn phi phi bit khi no, u, nh th no v ti sao h li thc hin truy cp ny. Nhiu cng c h tr c xy dng, cho php cc cng ty gim st truy cp hay cc hot ng trn c s d liu. Bn c th dng sn phm ca Imperva Inc., Guardium Inc., Application Security Inc. v Lumigent Technologies Inc. Chng c thit k nhm mc ch gip bn bit ngi dng hay admin no ang lm vic trn c s d liu vi c quyn truy cp, hay chnh sa, copy, xo, download s lng ln tp hp cc file, hoc a ra cc cnh bo khi ai c gng thc hin mt trong cc hot ng trn. Cc sn phm ny cng cung cp du vt kim tra kh r rng theo di khi c ngi vi phm quy nh ca doanh nghip. M ho d liu nhy cm trong c s d liu l mt phng php khc ng xem xt. 4. Gii hn c quyn ngi dng Hu ht cc cng ty u cung cp nhiu c quyn cho ngi dng hn so vi cn thit. l nhn nh ca Amichai Shulman, gim c cng ngh ca Imperva. Gim st truy cp d liu cc k quan trng ca ngi dng v theo di truy cp khng xc nh vi d liu mc nguy him cao l nhng bc khng th thiu. To quy nh truy cp nhm gii hn c quyn mng ca ngi dng mt cch cht ch. Ch cho php truy cp lp d liu tng ng cn thit cho cng vic ca tng kiu ngi dng, ng thi thit lp cc iu khin nhm bt buc nhn vin trong cng ty phi tun th quy nh ni b xy dng. V d, a ra cnh bo khi ai vn bnh thng ch lm vic vi 10 tp ti liu mi ngy, t nhin bt u truy cp s vi lng ln hn. Vic a ra quyt nh iu khin truy cp cho thnh vin ni b v ngi ngoi l kh n gin, Matt Kesner - gim c cng ngh ca Fenwick & West LLC, hng lut c tr s ti Califoocnia (M) khng nh. Nhng i khi ngi bn ngoi li cn truy cp hp php d liu ca doanh nghip vi s lng ngang bng hoc thm ch ln hn nhu cu ca nhn vin ni b. V d, cc mng Extranet client ca Fenwick & West ang c s dng thng xuyn bi khch hng hp tc vi nhn vin u quyn ca hng. i khi, ngi dng bn 10. 10ngoi hng th vi d liu ca doanh nghip hn nhiu so vi ngi trong ni b cng ty. 5. Quan tm ti cc im cui S pht trin nhanh chng ca th trng thit b di ng nh laptop, cc my xch tay khc, th nh USB hay my nghe nhc iPod ngy cng to iu kin cho nhng k c xu trong ni b cng ty n cp d liu d dng hn. Cc cng ty cn phi pht trin hot ng iu khin v gim st tp trung ho. Trong , thit b phi c gn vo mng v h thng doanh nghip, quy nh r d liu no c download, upload hay lu tr ti u. Thc hin c cc cng vic ny l c mt thch thc. Nhng bn khng cn qu lo lng, v mt s sn phm ca cc hng nh Code Green Networks Inc., ControlGuard Inc. v SecureWave SA s gip bn d dng hn khi tin hnh cc hot ng mong mun. Trc y, c rt t cng ty t cc kim sot hiu qu vo ng ni cn thit cho php h gim st h thng ni b mt cch cht ch v theo di c qu trnh di chuyn hay truyn vn ca d liu, Alex Bakman - gim c iu hnh ca Ecora Software Corp khng nh. iu c ngha l hot ng ph hoi tng din ra khng kn khng trng trong sut thi gian di. 6. Tp trung ho d liu bn quyn tr tu i vi mt cng ty ln, vic bo v bn quyn tr tu ri rc trn nhiu h thng l iu khng th. Do , lu tr cc d liu ny trong mt h thng th vin ti nguyn tp trung ho bt c khi no c th l bin php an ton v tin li trong trong bo mt cng nh chia s thng tin. Thng thng, ngi ta t tt c trng vo trong mt r, Ira Winkler - chuyn vin t vn bo mt t do v ph trch chuyn mc Computerworld.com v von. Nhng trong trng hp ny, bo v mt h thng s d dng hn l bo v v s h thng con nm ri rc ca n.Cu hi v bi tp:1. Trnh by cc phng php nh gi cht lng h thng ATTT.2. Phn tch nhng nguyn nhn a n thng tin trn a b mt ? Nu cc bin php khc phc.3. Phn tch nhng nguyn nhn a n r r thng tin trn my tnh? Trnh by cc bin php khc phc. 11. 11BI 2Tn bi : LU TR H THNG THNG TIN TRN CC THIT B LU TRM bi : ITPRG03-19.2Gii thiu : Lu tr d liu an ton v khoa hc l vic rt quan trng trong lnh vc cng ngh thng tin. Bi hc cung cp cc kin thc c s v hnh thc, cch thc v thit b lu tr, phc hi bo v h thng d liu.Mc tiu thc hin:- S dng c cc thit b lu tr thng dng- Sao lu d liu di nhiu hnh thc.- Phc hi d liu trong mt s trng hp- S dng c mt s phn mm tin ch v phn mm cng c phc hi, bo v cho h thng thng tin.Ni dung chnh:I. Cu trc ca th mc v tp tin trn my n v trn h thng mng my tnh.1. T chc aT chc a l mt trong nhng c trng c bn ca h iu hnh. a mi mua hoc a s dng vi mt iu hnh khc khng tng thch vi h iu hnh ang s dng th khng th dng c. Lc ny ta phi tin hnh t chc a cho c cu trc m h iu hnh hin ang dng hiu c.T chc a cho php qun l c cc d liu c ghi trn a nh cc tp tin, qun l vng nh, c/ghi thng tin,...Vic t chc a thng c tin hnh bng chng trnh nh dng a: FORMAT. Khi gi chng trnh ny bng lnh FORMAT chng trnh s t ng thi hnh cc bc cn thit t chc a (nh dng a).Chng trnh ny t chc a nh sau :- To ra cc rnh (track) trn b mt a, chia s sector trn 1 rnh, nh s Byte trn mi sector.- Sao chp to tp tin mi (boot record)- To bng cp pht a cho tp tin: bng FAT- To th mc gc (root directory)- Xc nh vng ghi tn, vng lu tr d liu. a trc khi s dng phi c nh dng (format) mi c th lu tr d liu ln c. Mi h iu hnh c cch t chc a ring. HH Windows 98 t chc cu trc a theo dng FAT (file allocation table). Khi nh dng a, HH s chia mi mt a ra thnh nhng ng trn ng tm (track) c nh s t ngoi vo trong v bt u t 0. 12. 12 Mi track c chia thnh nhiu on nh gi l cung t (sector), cc cung t c nh s bt u t 1. Mi cung t thng cha 512 bytes. D liu s c lu trn tng cung t.Hnh 1 .2: cch phn chia mi mt a khi c nh dng.2. Th mc v tp tin2.1 Tp tin:a) Tp tin (file) :Tp tin l hnh thc, n v lu tr thng tin trn a ca h iu hnh. Ni dung ca tp tin l thng tin cn lu tr. Tp tin (vit tt cho tp thng tin; cn c gi l tp, tp tin, file) l mt tp hp ca thng tin c t tn. Thng thng th cc tp tin ny cha trong cc thit b lu tr nh a cng, a mm, CD, DVD cng nh l cc loi chip in t dng k thut flash c th thy trong cc nh c giao din USB. Ni cch khc, tp tin l mt dy cc bit c tn v c cha trong cc thit b lu tr d liu k thut s.b) c im Mt tp tin lun lun kt thc bng 1 k t c bit (hay du kt thc) c m ASCII l 255 h thp phn. K t ny thng c k hiu l EOF ( End Of File). Mt tp tin c th khng cha mt thng tin no ngoi tr tn v du kt thc. Tuy nhin, iu ny khng h mu thun vi nh ngha v bn thn tn ca tp tin cng cha thng tin. Nhng tp tin ny gi l tp tin rng hay tp tin trng. di (kch thc) ca tp tin c th ch ph thuc vo kh nng ca my tnh, kh nng ca h iu hnh cng nh vo phn mm ng dng dng n. n v nh nht dng o di ca tp tin l byte. di ca tp tin khng bao gm di ca tn tp tin v du kt thc.c) Thuc tnhNhng c tnh v gii hn ca tp tin gi l thuc tnh ca tp tin.Cc loi thuc tnhTy theo h thng tp tin m cc thuc tnh ny c th khc nhau.Th d cc thuc tnh trn h thng tp tin FAT bao gm: Archive: lu tr. Trn cc h iu hnh DOS th thuc tnh ny c nh khi mi khi tp tin b thay i, v b xa khi thc hin lnh backup sao lu d liu. Hidden: n. Khi mt tp tin c thuc tnh ny th cc chng trnh lit k cc tp tin theo mc nh s b qua, khng lit k tp tin ny. Ngi s dng vn c th lm vic trn tp tin ny nh bnh thng. Read-only: ch c. Khi mt tp tin c thuc tnh ny th cc chng trnh x l tp tin theo mc nh s khng cho php xa, di chuyn tp tin hoc thay i ni dungTrackSector 13. 13tp tin. Cn cc thao tc khc nh i tn tp tin, c ni dung tp tin vn c cho php. System: thuc v h thng. Mt tp tin c thuc tnh ny s chu cc hn ch bao gm cc hn ch ca thuc tnh Hidden v cc hn ch ca thuc tnh Read-only, ngha l khng b lit k, khng th xa, di chuyn, thay i ni dung. Thuc tnh ny ch yu dng cho cc tp tin quan trng ca h iu hnh. Sub-directory (hay directory): th mc con. Nhng tp tin c thuc tnh ny c x l nh l th mc. Th mc l tp tin dng c bit, ni dung khng cha d liu thng thng m cha cc tp tin v cc th mc khc. Ngoi ra, cn rt nhiu thuc tnh khc ca cc tp tin m ty theo h iu hnh s c nh ngha thm vo. Th d i vi h iu hnh Linux cc tp tin c th c thm cc thuc tnh nh cc quyn s dng tp tin, c im ca tp tin, v thng tin v cc loi tp tin nh l cc loi tp tin lin kt mm, cc socket, cc pipe ...Lu : Cc thuc tnh ca mt tp tin thng khng nh hng n ni dung thng tin ca tp tin nhng li nh hng rt nhiu n chc nng v vic x dng tp tin. Th d cc tp tin khng c thuc tnh cho php thi hnh th khng th xem l mt phn mm kh thi c mc d ni dung ca n c th ch cha cc ch th my tnh. Cch lm tp tin tr nn kh thi l thay i thuc tnh kh thi ca n hay l phi thay i phn ui ca tn tp tin (nh l trng hp ca h iu hnh Windows - DOS)d) nh dngCu trc ca mt tp tin nh ngha cch thc m tp tin c cha, c thc thi, v th hin trn cc thit b (nh mn hnh hay my in) gi l nh dng ca tp tin. nh dng ny c th n gin hay phc tp.nh dng ca tp tin ph thuc vo nhiu yu t trong quan trng nht bao gm: H iu hnh khc nhau v kin trc my tnh khc nhau c th i hi cc nh dng cho tp tin mt cch khc nhau.Th d: Trn cng mt kin trc Intel, tp tin vn bn dng n gin nht to nn bi h iu hnh Linux cng c s khc nhau vi tp tin vn bn ca Windows (hay DOS). D nhin, cc tp tin vn bn ny li cng khng th c c trn cc my dng h iu hnh Mac OS (chng khc nhau hon ton v mt kin trc my tnh) nu khng c cc tin ch c bit chuyn i nh dng. Tp tin dng cho cc mc tiu khc nhau cng s c cc nh dng khc nhau. Ngoi s rng buc v nh dng ca h iu hnh, cc tp tin dng trong cc ng dng hay cc phn mm khc nhau cng s khc nhau v s khc nhau ny ty thuc vo kin trc ca cc ng dng x dng cc tp tin .Th d d hiu nht l nh dng ca mt tp tin vn bn phi khc vi nh dng ca mt tp tin hnh nh hay tp tin m thanh. Cc tp tin dng cho cng mt mc tiu cng c th c nh dng khc nhau tu theo nh sn xut no thit k ra n.Th d: Trong cc tp tin hnh v ha th cc tp tin kiu Bitmap (cc tp hnh c ui l .bmp) c nh dng hon ton khc vi cc tp tin kiu Tagged Image File Format (ui ca lai tp tin ny l .tif) v cng khc vi tp tin kiu Joint Photographic Experts Group (vi cc ui c dng .jpg hay .jpeg).e) Tn Ty theo h iu hnh m c th c cc qui c v tn tp tin. di ca tn tp tin ty thuc vo h thng tp tin. Ty thuc vo h thng tp tin v h iu hnh m s c mt s k t khng c dng cho tn tp tin.Th d: Trn h iu hnh Microsoft Windows, khng c dng cc k t sau trong tn tp tin:/ : * ? " < > |Theo truyn thng c ca h thng DOS v Windows, tn tp tin thng bao gm hai phn: phn tn v phn m rng (cn gi l phn ui). Tuy nhin, tn ca mt tp tin khng nht thit phi c phn m rng ny. 14. 14Th d v cu trc bit ca tp tin ASCIIHnh 1.3 : cu trc bit ca tp tin ASCIITrong hnh trn l hai tp tin vn bn dng n gin dng m ASCII. Tp tin "hoso.txt" l tp tin son ra bng lnh edit ca h iu hnh Windows. Tp tin th nh, "hoso2.txt", li c son tho bng lnh vi trong h iu hnh Linux. Hy lu qui c xung hng ca tp tin trong Windows s bao gm hai byte: du CR (cariage return) c gi tr ASCII l 0x0D v du LF (line feed) c gi tr 0x0A; trong khi , Linux ch cn du LF l . iu ny cho thy s khc nhau v nh dng.2.2 Th mcTh mc (Directory, FOLDER) :Khi s lng tp tin trn a nhiu n hng trm, hng ngn tp tin th vic tm li mt hay mt nhm cc tp tin no s kh khn. d dng tm kim, cn to cc th mc cha cc tp tin cng ch , chc nng vo trong mt th mc.Th mc l hnh thc, n v qun l tp tin ca h iu hnh. Ni dung ca th mc l cc tp tin m n qun l.Cc th mc trn a c t chc theo dng phn cp, cc th mc xut pht t mt th mc chnh trn a gi l th mc gc (root directory). V cch t chc th mc trn a ging nh mt ci cy nn s th mc trn a gi l cy th mc (directory tree).Th mc gc c k hiudo chng trnh nh dng a to ra. Cc th mc c to trong qu trnh lm vic gi l cc th mc con (subdirectory).Trn a khng c sn cy th mc ca n. Khi nh dng a h iu hnh to ra th mc gc. Sau ngi s dng s to ra cc th mc con khi cn. Mt s th mc c cc chng trnh to ra trong lc ci t. Cc tp tin nn c t trong th mc con, ng t ngay vo th mc gc.Mt khi s lng tp tin c lu tr trn b nh ngoi ln ti 1 con s kh ln th nht thit phi a ra khi nim th mc. Khi nim ny cng gn ging nh h thng th mc trong th vin (khi mi tp tin c th v nh 1 cun sch).Nu s sch khng l trong th vin khng c t chc theo mt trt t hp l m c chung vo mt ch th khi mun tm 1 cun sch (theo 1 ch no m ta cha bit tn ca cun sch chng hn), ta phi nhn vo tng cun mt, v khng phi th nhn tip qua cun khc cho n khi tm c. Cch lm c th khin ta phi mt 1 khong thi gian rt kinh khng, nht l khi cun sch mun tm khng c trong th vin th ta vn phi xem ht tt c mi cun sch trong th vin mi bit c l khng c! khc phc tr ngi ngi ta t chc h thng th mc: danh mc tn sch c lit k theo tng ch , trong mi ch li c th c nhiu ch con. Vic t chc phn cp dng cy nh vy chc chn s gip cho thi gian tm kim 1 cun sch theo 1 ch no d cha bit tn sch cng s rt nhanh.Ni dung cc tp tin cn a dng hn ni dung ca cc quyn sch (khng ch l ti liu vn bn bnh thng m cn c th l hnh nh, m thanh, nhc, phim, tr chi, chng trnh cc loi...), v s lng tp tin trn b nh ngoi cng rt nhiu khin cho vic tm kim & s dng chng cng s rt kh khn nu nh ta cng chung vo 1 ch m khng t chc 15. 15theo mt trt t hp l. Do t chc h thng th mc phn cp trn b nh ngoi l rt cn thit, gii quyt nhu cu trn.Tm li, khi nim th mc cng c a ra bi h iu hnh, vic tm kim & s dng tp tin c hiu qu. Mi th mc c th cha cc tp tin v cc th mc con bn trong (d nhin trong mi th mc cng c th ch cha ton tp tin, hoc ch cha ton th mc con, hoc ang l th mc rng khng cha g c).II. Cch lu tr d liu qua h thng bng FAT (FAT 16, FAT 32, FAT NTFS...)T chc h thng tp tin trn a1. Cc nhn xt & phn tch cn thit: c th lu tr c thng tin /d liu vo a & truy xut, s dng c cc d liu trn a mt cch hiu qu th cn phi a ra nhng phn tch, nhn xt sau:i) Phi xc nh cc v tr cn trng ( c th lu d liu vo a) ii) Mi sector (hoc tng qut hn l mi block) ch thuc ti a 1 tp tin, tc nu sector cha ni dung ca 1 tp tin th trong sector s khng c ni dung ca tp tin khc ( d qun l, khng b nhm ln thng tin gia 2 tp tin) iii) Tn & cc thuc tnh ca tp tin cn c lu ring vo 1 vng ( tc truyxut d liu nhanh hn) iv) Phi c thng tin v tr bt u ca ni dung tp tin (do phn tch trn) v) Ni dung tp tin khng bt buc phi lin tc (phi cho php c lu tr vocc vng khc nhau khi cn phn mnh) vi) Phi bit cc v tr cha ni dung tp tin (do phn tch trn) vii) Phi bit cc v tr b h viii) Ni dung tp tin nn lu tr theo n v l CLUSTER (l dy N sector lin tip d qun l & vic truy xut c nhanh hn)2. Cluster2.1. Khi nimn v c ghi trn a l sector, nhng n v lu tr ni dung tp tin khng phi l mt sector m l mt cluster gm N sector lin tip i v tr lu gi ni dung tp tin trong cc phn tch trn s tn ti trn vng d liu (vng DATA) ni cha ni dung tp tin.2.2. L do pht sinh khi nim Clusteri) Nu sector trn vng d liu qu nhiu th c th s kh hoc khng qun l c, khi qun l trn cluster s d dng hiu qu hn.ii) Ni dung tp tin thng chim nhiu sector v c th khng lin tc, v thi gian c ghi mt ln n sector lin tip thng nhanh hn nhiu so vi thi gian c ghi n ln m mi ln ch 1 sector. Do ti u thi gian truy xut tp tin th cn chn n v truy xut l mt khi nhiu sector.2.3. Hnh thc t chca s c chia thnh 2 vng: vng d liu (DATA) cha ni dung tp tin v vng h thng (SYSTEM) cha cc thng tin qun l. Vng SYSTEM c kch thc nh hn nhiu so vi vng DATA v phi truy xut mi khi s dng a nn thng nm ngay u a, phn cn li thuc v vng DATA. Trn vng DATA l mt dy cc Cluster lin tip c nh ch s theo th t tng dn (bt u t 0, 1 hay 2 ty theo H iu Hnh). Nh vy nu vng DATA c SD sector & bt u ti sector SS, mi Cluster chim SC sector, Cluster u tin c nh ch s l FC, th a s c tng cng SD/Sc Cluster v Cluster C s bt u ti sector: SS + (C FC ) * SCV d, nu a c kch thc 4014 sector, vng SYSTEM chim 11 sector, mi cluster chim 4 sector, Cluster u tin c nh ch s l 2; th phn b Cluster trn a s nh sau:Cluster 2Cluster 3Cluster 4...Cluster 1001 ... ... 16. 160 1 ... 10 SYSTEM AREA11 12 13 14 15 16 17 18 19 20 21 22 DATA AREA... 4007 4008 4009 4010Hnh 1.4 : phn b Cluster trn a( 3 sector 4011, 4012, 4013 s khng thuc cluster no v khng c s dng)2.4. Kch thc ClusterS sector trn 1 cluster nn l ly tha ca 2 v c gi tr ln hay nh l ty theo a. Nu ta chn kch thc cluster cng ln th s cng lng ph a v mt tp tin c kch thc nh vn phi dng mt cluster gm nhiu sector lu, nhng khi s hn ch c s phn mnh ca tp tin v v vy tp tin c th an ton hn & truy xut nhanh hn. Kch thc ca Cluster ph thuc vo kh nhiu yu t: dung lng a, tc truy xut 1 dy sector trn a, kch thc ca a s tp tin s lu vo a, s cluster ti a m h thng c th qun l, nhu cu ca ngi s dng, Trn cc a cng hin ti th Cluster thng c kch thc 4, 8 hoc 16 sector.V d:-Vi a mm 1.44 MB bnh thng (c 2880 sector), nu ta cho 1 cluster chim 1000 sector th s rt khng hp l. V khi ta ch c th chp c ti a 2 tp tin vo a, du mi tp ch c kch thc l 1byte! Tuy nhin nu ta ch ton chp vo a cc tp tin c kch thc gn 1000 sector th s khng cn s lng ph na.-Vi h thng ch c th qun l ti a M Cluster, nu vng DATA ca a c 100M sector th ta phi cho mi Cluster ti thiu 100 sector mi c th qun l c ton b vng DATA3. Bng qun l Cluster3.1. Khi nimL 1 dy phn t, mi phn t thng l 1 con s nguyn c dng qun l 1 cluster trn vng d liu. Vic qun l y c th l cho bit cluster tng ng ang trng thi trng, h, hay ang cha ni dung ca 1 tp tin, v cho php xc nh danh sch cc cluster cha ni dung ca tp tin. C th dng 1 bng p ng cc nhu cu trn, nhng cng c th t chc nhiu bng mi bng phc v cho 1 nhu cu.3.2 L do pht sinh a ni dung tp tin vo a th phi xc nh cc cluster cn trng (phn tch (i)), c ni dung tp tin trn a th phi xc nh c danh sch cc cluster cha ni dung tp tin (phn tch (vi)), tuy c th lu thng tin qun l ngay trn cluster nhng khi truy xut rt chm nn nht thit phi lp ra bng ny qun l truy xut nhanh hn.3.3. Hnh thc t chc xc nh cc cluster trng, h, hay thuc trng thi lun l c bit no (nhng trng thi ch mang 1 trong 2 gi tr: C Khng) ta c th qun l theo dng ch mc: mi phn t ca bng qun l l 1 con s ni ln trng thi ca cluster mang ch s tng ng. mc n gin ta ch cn qun l 2 trng thi lun l l cluster trng & cluster h. Danh sch cc cluster h c th lu trc tip (c bao nhiu cluster h th danh sch c by nhiu phn t), v s cluster h trn a s rt t. Vic qun l cluster trng c th dng hnh thc bitmap (mi bit qun l 1 cluster tng ng): nu mun bit cluster K l trng hay khng ta xem gi tr ca bit K l 0 hay 1. Ta cng c th qun l vng trng bng cch lu 1 danh sch cc phn t, mi phn t cha v tr bt u & kch thc ca vng trng tng ng.Vic xc nh mt trng thi lun l ca cluster c th thit k kh n gin, vn ch yu l hnh thc t chc c th xc nh chui cc cluster cha ni dung ca 1 tp tin, c mt s hnh thc c bn nh sau:1. 3.3.1 Lu tr ni dung tp tin trn dy cluster lin tip ...2. 3.3.2 S dng cu trc danh sch lin kt ...3. 3.3.3 S dng cu trc danh sch lin kt kt hp ch mc: 17. 17Ta t chc 1 bng cc phn t nguyn (dy s nguyn), mi phn t c dng qun l 1 cluster trn vng d liu theo dng ch mc (phn t K qun l cluster K). Vi qui nh:. Nu phn t K trn bng c gi tr l FREE th cluster K trn vng d liu ang trng thi trng.. Nu phn t K trn bng c gi tr l BAD th cluster K trn vng d liu s c h thng hiu l trng thi h.. Nu phn t K trn bng c gi tr khc FREE v khc BAD th cluster K trn vng d liu ang cha ni dung ca 1 tp tin. Khi ny ta cn bit c cluster k tip cha ni dung ca tp tin: nu phn t K ca ba?ng c gi tr L v L = EOF th cluster K l cluster cui cng ca tp tin, nu L EOF th phn k tip ca ni dung tp tin nm ti cluster L (qun l theo dng danh sch lin kt).Nh vy hnh thc t chc ny c th p ng c tt c cc nhu cu qun l cluster: xc nh cluster trng, h, hay ang cha ni dung tp tin, v chui cc cluster cha ni dung ca mt tp tin (khi bit cluster bt u).V d, nu ni dung bng qun l Cluster ca a trn nh sau:Hnh 2.4: Bng qun l Cluster trn a0 1 2 3 4 5 6 7 8 9 10 11 12 13 ... 1001(cc phn t t 13 n 1001 u c gi tr l FREE)th t y c th xc nh lc ny trn a ang c 2 cluster h, 990 cluster trng, 8 cluster chani dung tp tin. C th l:-Cc cluster h: 4, 10-Cc cluster trng: 8, 13, 14, 15, , 1001-Cc cluster cha ni dung tp tin: 2, 3, 5, 6, 7, 9, 11, 12. Trong c 3 tp tin: + tp tin I chim 3 cluster theo ng th t l: 2, 3, 5. + tp tin II chim 1 cluster duy nht l: 6. + tp tin III chim 4 cluster theo ng th t l: 9, 7, 11, 12.Lu : Phn t u tin ca bng c ch s l 0 nn nu Cluster u tin ca vng DATA c nh ch s l FC > 0 th FC phn t u tin ca bng (t 0 .. FC -1) s khng c dng qun l Cluster, m bo tnh cht ch mc (phn t mang ch s K qun l trng thi ca Cluster mang ch s K). Khi ny khng gian b lng ph hon ton khng ng k, nhng vic qun l truy xut th tin li hn, ta cng c th tn dng phn khng gian tng ng vi FC phn t u bng ny lu 1 thng tin qun l no .Gi tr ca cc phn t trn bng:Ta cn phi t ra 3 gi tr hng c bit l FREE, BAD v EOF tng ng vi 3 trng thi cluster: trng, h, hoc l cluster cui ca ni dung tp tin, ta cng c th t thm 1 s gi tr c bit na cho nhng trng thi c bit khc ca cluster (nu c) hoc 1 s gi tr dnh ring phc v cho nhng nhu cu trong tng lai. Nhng gi tr cn li s tng ng vi trng thi cluster ang cha ni dung tp tin v lc gi tr ca phn t cng chnh l ch s ca cluster k tip.Cc hng c bit (v dnh ring nu c) phi khc vi cc gi tr c th c trn ch s cluster th cluster tng ng mi c th s dng c. V d, vi hnh trn, nu ta t hng EOF = 7 th tp tin III s b hiu lm l ch chim ng mi cluster 9 ch khng phi chim 4 cluster!Mi phn t trn bng nn l 1 con s nguyn dng c th qun l c nhiu cluster hn, khi ny cc hng c bit nu trn s khng th l s m m phi chim nhng gi tr ln nht c th biu din c, v ch s ca cluster cui cng trn vng DATA buc 18. 18phi nh hn nhng gi tr hng c bit ny. Trong trng hp cluster u tin c nh ch s l FC v FC > 0 th cng c th s dng cc gi tr 0..FC-1 cho nhng hng c bit trn.3.4. Kch thc ca bng qun l ClusterMi phn t trn bng l 1 con s nguyn nn pht sinh vn phi lu tr mi s nguyn bng bao nhiu bit. Ta c th cn c vo ch s cluster cui cng trn vng DATA xc nh gi tr ti a cn biu din c ca mi phn t v gi tr ca cc hng c bit suy ra s bit ti thiu ca mi phn t, n gin c th dng 16bit hoc 32bit cho mi phn t ty theo a c kch thc nh hay ln. Vn phc tp nm ch lm sao xc nh s phn t ca bng, cng nh s cluster trn vng DATA. V khi to (nh dng) a th ta ch c kch thc ca a, ch khng c kch thc vng DATA, v khng th t t ra kch thc cho n nh vi nhng thnh phn khc. Ta c th gii quyt bng cch gi nh kch thc ca bng l 1 sector & kim chng li xem c hp l hay khng, nu khng th tng dn kch thc ca bng cho n khi hp l.3.5. T chc qun l cluster trn h iu hnh DOS & Windows 9xBng qun l cluster trn DOS & Windows 9x c gi l FAT (File Allocation Table), c t chc theo hnh thc danh sch lin kt kt hp ch mc. Trn DOS mi phn t ca bng FAT c biu din bng 1 con s nguyn 12bit hoc 16bit (bng FAT tng ng c tn l FAT12 hoc FAT16). Trn Windows cng c 2 loi FAT trn v c thm loi FAT32 (mi phn t c lu bng 32bit).Nu phn t K ca FAT c gi tr L th trng thi ca Cluster K l:Trng thi ca Cluster K Gi tr ca L FAT12 FAT16 FAT32Trng000HFF7FFF7FFFFF7Cluster cui ca tp tinFFFFFFFFFFFFFCha ni dung tp tin v c cluster k sau l L2 .. FEF2 .. FFEF2..FFFFEFHnh 1.5 : Trng thi ca Cluster KC mt s gi tr tuy vn thuc phm vi biu din nhng khng th c vi L (v d, vi FAT12 l cc gi tr 1, FF0 .. FF6, FF8 .. FFE), y l cc gi tr dnh ring c d phng c th s dng cho nhng trng thi c bit khc ca cluster trong nhng phin bn sau ca h iu hnh, khi s vn c c s tng thch gia cc phin bn c & mi. Chnh v gi tr 0 c dng biu din trng thi cluster trng nn s khng th tn ti cluster mang ch s 0 trn vng d liu, DOS & Windows nh ch s ca cluster u tin trn vng d liu l 2 (FC = 2)Cng t nhng gi tr tng ng vi trng thi cluster cha ni dung tp tin bng trn, ta c th suy ra s cluster ti a m bng FAT12 c th qun l c l FEE (tc 4078d, ch khng phi l 212 = 4096), v FAT16 l FFEE (tc 65518d). Nh vy nu s cluster trn DATA khng qu 4078 th h thng s dng FAT12 qun l, nu s cluster ln hn 4078 nhng khng qu 65518 th s dng FAT16, v ln hn 65518 th s dng FAT32. Tuy nhin l qui c mc nh ca h iu hnh, ta cng c th ch nh loi FAT cn s dng, v d vng DATA c 2004 cluster th dng FAT16 qun l vn c.Bng qun l cluster rt quan trng nn DOS & Windows thng lu thm N bng backup phng trnh h hng (N0, thng l 1). Cc bng FAT c lu tr k tip nhau trn 1 vng gi l vng FAT. 19. 19Vi bng FAT12, vic truy xut mt phn t hi phc tp: n v truy xut trn RAM l 1 byte nhng mi phn t li c kch thc 1.5 byte. Ta c th xc nh 2 byte tng ng cha gi tr ca phn t, ly gi tr s nguyn khng du 2byte ti ri dng cc php ton x l trn bit truy xut c con s 1.5 byte tng ng.V d, ni dung 12 byte u ca bng FAT l:F0 FF FF 03 40 00FF7FFFABCDEFoffset 0 1 2 3 4 5 6 7 8 9 A Bth 8 phn t u tng ng ca bng FAT l:FF0 FFF 003 004 FFFFF7DABEFCphnt 0 1 2 3 4 5 6 7V kch thc bng FAT12 l kh nh (ti a 12 sector) nn vic truy xut 1 phn t c n gin ngi ta thng c ton b cc sector trn bng FAT vo 1 vng m ri t vng m ny xy ng ra 1 mng s nguyn 2byte m mi phn t ca mng mang gi tr ca phn t tng ng trn bng FAT. Khi cn lu bng FAT vo a th li thc hin thao tc ngc li: t mng s nguyn 2 byte to ra dy byte tng ng ca FAT a vo vng m v lu vng m vo cc sector cha FAT trn a.4. Bng th mc4.1 Khi nim v RDET (Root Directory Entry Table):L 1 dy phn t (entry), mi phn t cha tn & cc thuc tnh ca 1 tp tin trn th mc gc ca a (hoc l phn t trng cha thuc v 1 tp tin no ht).V d, nu m hnh thuc tnh tp tin c thit k ch gm cc thnh phn: tn chnh (chui ti a 4 k t), tn m rng (chui ti a 2 k t), kch thc tp tin (s nguyn 2 byte) th RDET s nh sau:OffsetHnh 1.6 : RDET4.2 L do pht sinh khi nim RDETT phn tch (iii).4.3 Kch thc RDETS entry trn RDET c qui nh bi chng trnh nh dng (format) a, con s ny s ln hay nh l ty theo dung lng ca a (nhng chc chn l s khng qu ln v s tp tin trn a d rt nhiu th s tp tin th mc gc cng khng nn qu nhiu, s gy kh khn cho vic qun l ca ngi s dng). S entry trn RDET khng bt buc phi l 1 gi tr chnh xc m cho php dao ng mt t, v vy ta c th iu chnh hn ch lng ph khng gian lu tr trn sector. V d, nu mi entry c kch thc 32 byte & ta d nh t chc 50 entry cho RDET th khng hay lm, c th iu chnh li thnh 48 entry hoc 64 entry. 20. 204.4 Cu trc Entry ca DOSArchiveDirectoryaLabelSystemHidden ReadOnly + ReadOnly: thuc tnh ch c, khi tp tin c thuc tnh ny h thng s khng cho php sa hoc xa. + Hidden: thuc tnh n, trng thi mc nh h thng s khng hin th tn ca cc tp tin ny khi lit k danh sch tp tin. + System: thuc tnh h thng, cho bit tp tin c phi thuc h iu hnh khng + a Label: thuc tnh nhn a, trn RDET ch c ti a 1 entry c thuc tnh ny, khi entry khng phi tng ng vi tp tin m c dng cha nhn ca a l 1 chui ti a 11 k t c lu 11 byte u tin ca entry + Directory: thuc tnh th mc, nu entry c thuc tnh ny th tp tin tng ng khng phi l mt tp tin bnh thng m l mt tp tin th mc. Mi th mc trn DOS c lu tr ging nh mt tp tin bnh thng, ni dung ca tp tin th mc ny l danh mc nhng tp tin v th mc con ca n. + Archive: thuc tnh lu tr, cho bit tp tin c backup hay cha (bng lnh backup ca h iu hnh), y l thuc tnh hu nh khng c s dng v t khi c nhu cu backup tt c cc tp tin m ch cn lu nhng tp tin cn thit.Khi ta xa tp tin, entry tng ng phi c chuyn sang trng thi trng, nhng 21. 21trng thi trng lc ny khng phi l 32 byte ca entry c chuyn sang gi tr 0 m ch c byte u tin c i thnh E5. V tt c cc k t ca tn tp tin u khng th c m l 0 hoc E5 nn bit 1 entry c trng hay khng ta ch cn nhn gi tr byte u tin ca entry: nu khc 0 v E5 th khng phi l entry trng. Mi khi tm entry trng s dng h thng tm theo th t t u tr i nn nu ta gp 1 entry trng c byte u l 0 th tt c cc entry pha sau cng l nhng entry trng dng cha tng uc s dng (32 byte trn entry u l 0)4.5 Bng th mc con SDET (Sub Directory Entry Table):4.5.1 Khi nim:Mi th mc trn DOS c lu tr ging nh mt tp tin bnh thng. Ni dung ca tp tin th mc ny l mt dy entry, mi entry cha tn & thuc tnh ca nhng tp tin v th mc con thuc th mc ang xt ging y nh cc entry trn RDET, dy entry ny c gi l SDET. C th ni mt cch n gin rng SDET l ni dung ca tp tin th mc. SDET c cu trc t chc ging nh RDET nhng c lu tr ngay trn vng DATA (v l ni dung tp tin). Trn a c ng 1 RDET nhng c th c rt nhiu SDET v cng c th khng c bng SDET no.4.5.2 L do pht sinhNu s tp tin trn a c th nhiu th nht thit phi a ra khi nim th mc trnh chuyn tt c mi tp tin trn a phi lu chung vo 1 ni rt kh qun l. V cc thuc tnh ca th mc kh ging vi cc thuc tnh ca tp tin bnh thng nn c th t ra khi nim th mc l mt tp tin c bit v t chc lu tr nh mt tp tin bnh thng, khng cn phi a ra mt thit k khc cho vic t chc lu tr h thng th mc.4.5.3 Kch thc SDETS entry trn SDET c th rt nh m cng c th rt ln, ph thuc vo s lng tp tin & th mc con bn trong th mc ang xt ch khng b qui nh 1 con s c nh nh trn RDET. V SDET nm trn vng DATA nn ti u s entry ca SDET thng c t sao cho khng b lng ph khng gian trn cluster. V d, nu entry c kch thc 32 byte v cluster c c kch thc 32 sector th s entry ca SDET s l bi ca 512.4.5.4 Bng SDET trn DOSLun c 2 entry . v .. u bng m t v chnh th mc ny v th mc cha ca n. Cu trc mi entry trn SDET cng ging nh entry trn RDET, ch khc s lng entry & v tr lu gi ni dung entry trn SDET l khng c nh. V SDET lun chim trn cluster nn thuc tnh kch thc tp tin trn entry tng ng vi th mc s khng cn s dng v lun c DOS gn l 0. Nh vy khi to 1 th mc th s entrytrong SDET ca th mc s l SC/32 (SC l kch thc cluster), trong entry u tin c phn tn l . v phn cn li lu cc thng tin v th mc ny, entry th hai c phn tn l .. (2 byte u ca entry lu k t . v 9 byte k sau lu khong trng) v phn cn li lu cc thng tin v th mc cha ca th mc ny, t entry th ba tr i u l entry trng (32byte u mang gi tr 0). Nu chp vo trong th mc con ny nhiu hn (SC/32 -2) tp tin th bng SDET hin ti khng s entry qun l, khi ny kch thc bng SDET s c h thng cho tng thm bng cch tm cluster trng trn vng DATA v lu ni dung cc entry pht sinh thm vo cluster mi ny (v phn cn li ca cluster nu c cng c lu cc entry trng nh trn cluster u tin).1. 5. Boot Sector2. 5.1 Khi nimL sector u tin ca a, cha mt on chng trnh nh np h iu hnh khi khi ng my v cc thng s quan trng ca a: kch thc cluster, kch thc bng th mc, kch thc bng qun l cluster, ...5.2 L do pht sinhCc bng qun l cluster & bng th mc p ng cc phn tch nu trn, nhng tht s c th thc hin c cc thao tc truy xut a ta cn phi bit c v tr & kch thc ca tng thnh phn trn a. V a c th c kt ni vo mt h thng khc nn thng tin v cc thnh phn ca a phi c lu ngay trn chnh a bt 22. 22c h thng no cng c th hiu. Sector u tin ca a l ni thch hp nht cha cc thng tin quan trng ny.5.3 Hnh thc t chcCc thng s quan trng ch chim 1 kch thc nh nn ta c th qui c mt vng nh trn sector dng cha cc thng s ca a (phn cn li l on chng trnh np h iu hnh khi khi ng), mi thng s c qui nh nm ti mt offset c th c nh no . Trong trng hp tng kch thc cc thng s v phn chng trnh np h iu hnh ln hn 512byte th c th dng tip nhng sector k sau lu5.4 T chc thng tin trong BootSector ca DOS & Windows5.4.1 Boot Sector ca h iu hnh DOS Offset S byte ngha0 (0h)3Lnh nhy n u on m Boot (qua khi vng thng s)3 (3h)8Tn cng ty /version ca HH11 (0Bh)2S byte ca sector13 (0Dh)1S sector ca cluster14 (0Eh)2S sector trc bng FAT16 (10h)1S lng bng FAT17 (11h)2S Entry ca RDET19 (13h)2S sector ca a21 (15h)1K hiu loi a22 (16h)2S sector ca FAT24 (18h)2S sector 1 track (tnh theo sector)26 (1Ah)2S lng u c (head)28 (1Ch)4Khong cch t ni m t a n u a32 (20h)4Kch thc a (nu s 2 byte ti offset 13h l 0)36 (24h)1K hiu vt l ca a cha a (0 : mm, 80h: cng)37 (25h)1Dnh ring38 (26h)1K hiu nhn din HH39 (27h)4SerialNumber ca a43 (2Bh)11a Label54 (36h)8Dnh ring62 (3Eh)448on chng trnh Boot np tip HH khi khi ng my510 (1FDh)2Du hiu kt thc BootSector /Master Boot (lun l AA55h)Hnh 1.7 : Boot Sector ca h iu hnh DOSV d, vi a c na u ca Boot Sector nh sau:EB 3C 90 4D 53 57 49 4E-34 2E 31 00 02 10 01 00 . 1 th lu tip vo cc v tr SB + SF , SB + 2*SF ,..., SB + (nF-1)*SF ) -Bc 5: To 1 vng m kch thc SR (byte) c ni dung cc byte u l 0. -Bc 6: Lu li vng m trn vo bng RDET trn a (lu vo SR sector bt u ti sector (SB + nF*SF ) )3. c ni dung tp tin trn a3.1 Khi nimy l thao tc truy xut a c thc hin nhiu nht, cng l thao tc thng 28. 28xuyn ca h thng my tnh. M tc truy xut b nh ngoi (ni cha tp tin) chm hn nhiu so vi b nh trong, do tng tc hot ng ca my tnh ng thi c th bo mt d liu, kim chng s hp l, khng vi cc s c c th gy h hng, ... khi truy xut tp tin ngi ta thng dng ti nhiu h thng Cache, nhiu k thut ti u & cc x l khc. Tuy nhin c th d dng hn cho vic nm c mt cch c bn t chc lu tr tp tin & c ch hot ng ca h thng qun l tp tin, cc thut gii c trnh by sau y ch nu cch gii quyt c bn, chn phng nht - khng quan tm nhiu n vic ti u & cc x l nng cao khc.Ta bit v c bn c 2 loi tp tin khc nhau: tp tin bnh thng v tp tin th mc (cn gi l th mc con). Cho nn trc mt c th thy c 2 thao tc khc nhau: c ni dung tp tin bnh thng & c ni dung bng th mc con (tc ni dung tp tin th mc). Nhng tht ra 1 tp tin bnh thng cng nh 1 th mc cng c th nm trong 1 th mc con no , v vy c th phn ra ti 4 thao tc tng i ring bit: c ni dung 1 tp tin bnh thng th mc gc ca a, c ni dung 1 th mc con nm th mc gc ca a, c ni dung 1 tp tin bnh thng 1 th mc con ca a, v c ni dung 1 th mc con nm trong 1 th mc con no ca a.3.2 c ni dung tp tin th mc gc ca a3.2.1 Thut gii:(u vo: tn a, tn tp tin cn ly ni dung; u ra: ni dung ca tp tin) Bc 1: c BootSector ca a xc nh cc thng s cn thit (v tr & kch thc ca bng th mc gc & bng qun l cluster, kch thc cluster, v tr bt u ca vng d liu,...) Bc 2: c bng th mc gc vo b nh. Bc 3: Tm trn bng th mc gc va c entry c phn tn ging vi tn tp tin cn ly ni dung (nu khng c th thng bo tp tin khng tn ti & thot). Bc 4: c bng qun l cluster vo b nh. Bc 5: T ni dung bng qun l cluster va c & thng tin ca entry tm c bc 3 suy ra danh sch nhng cluster cha ni dung tp tin. Bc 6: c nhng cluster tng ng vi danh sch trn & ghp cc ni dung c c li theo ng th t ta c ni dung tp tin (ring phn ni dung trn cluster cui ch ly N byte, vi N = MOD ).3.2.2 c ni dung tp tin th mc gc ca a c kin trc FAT12 /FAT16 -Bc 1: c BootSector xc nh cc thng s SB, SF, SR, SC, SS. -Bc 2: c bng RDET vo b nh. -Bc 3: Tm trn bng RDET va c entry c phn tn ging vi tn tp tin cn ly ni dung (nu khng c th thng bo tp tin khng tn ti & thot). -Bc 4: c bng FAT vo mng aFAT trn b nh. -Bc 5: T ch s cluster bt u f1 trong entry tm c bc 3 xc nh dy cc phn t k tip f2, f3, f4 , ... theo cng thc fi+1= aFAT [ fi ] cho n khi gp ch s fN c aFAT[ fN ] = EOF. -Bc 6: c nhng cluster f1, f2, f3 , ..., fN & ghp cc ni dung c c li theo ng th t ta c ni dung tp tin (ring phn ni dung trn cluster fN ch ly M byte, vi M = MOD SC ).3.3 c ni dung mt th mc con th mc gc ca aVic s dng ni dung tp tin bnh thng v ni dung ca tp tin th mc l hon ton khc nhau. Nhng nu t chc lu tr tp tin th mc ging nh tp tin bnh thng th vic c ni dung bng th mc con cng s ging nh c ni dung tp tin bnh thng. Ring i vi a c t chc theo cu trc FAT12 /FAT16 th phn ni dung tp tin th mc trn cluster cui cng c s dng ht ch khng nh tp tin bnh thng c th ch 29. 29chim 1 phn. V cng v vy trng trong entry ca tp tin th mc s khng c s dng (lun c gn l 0), d bng th mc c kch thc bao nhiu i na.3.4 c ni dung tp tin trong mt th mc con ca aEntry cha cc thng tin v tp tin cn c s