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Netapp Snapmirror Setup.

Snapmirror is an licensed utility in Netapp to do data transfer across filers.

Snapmirror works at Volume level or Qtree level. Snapmirror is mainly usedfor disaster recovery and replication. Snapmirrror needs a source and destination filer. (When source and destination are thesame filer, the snapmirror happens on local filer itself. This is when you have toreplicate volumes inside a filer. If you need DR capabilities of a volume inside a filer,you have to try syncmirror ).

Synchronous SnapMirror is a SnapMirror feature in which the data on one system is replicated on another system at, or near, the same time it is written to the first system. Synchronous SnapMirror synchronouslyreplicates data between single or clustered storage systems situated at remote sites using either an IP or a Fibre Channel connection. Before Data ONTAP saves data to disk, it collects written data in NVRAM.

Then, at a point in time called a consistency point, it sends the data to disk.

When the Synchronous SnapMirror feature is enabled, the source system forwards data to the destinationsystem as it is written in NVRAM. Then, at the consistency point, the source system sends its data to diskand tells the destination system to also send its data to disk.

This guides you quickly through the Snapmirror setup and commands.

1) Enable Snapmirror on source and destination filer

source-filer> options snapmirror.enable snapmirror.enable on source-filer> source-filer> options snapmirror.access snapmirror.access legacy source-filer>

2) Snapmirror AccessMake sure destination filer has snapmirror access to the source filer. The snapmirror filer'sname or IP address should be in /etc/snapmirror.allow. Use wrfile to add entries to

/etc/snapmirror.allow.

source-filer> rdfile /etc/snapmirror.allow destination-filer destination-filer2

source-filer>

3) Initializing a Snapmirror relation

Volume snapmirror : Create a destination volume on destination netapp filer, of same sizeas source volume or greater size. For volume snapmirror, the destination volume should bein restricted mode. For example, let us consider we are snapmirroring a 100G volume - wecreate the destination volume and make it restricted.

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destination-filer> vol create demo_destination aggr01 100G destination-filer> vol restrict demo_destination Volume SnapMirror creates a Snapshot copy before performing the initial transfer. Thiscopy is referred to as the baseline Snapshot copy. After performing an initial transfer of all data in the volume, VSM (Volume SnapMirror) sends to the destination only theblocks that have changed since the last successful replication. When SnapMirror performs an update transfer, it creates another new Snapshot copy and compares thechanged blocks. These changed blocks are sent as part of the update transfer.

Snapmirror is always destination filer driven. So the snapmirror initialize has to be done ondestination filer. The below command starts the baseline transfer.

destination-filer> snapmirror initialize -S source-filer:demo_sourcedestination-filer:demo_destination Transfer started. Monitor progress with 'snapmirror status' or the snapmirror log. destination-filer>

Qtree Snapmirror : For qtree snapmirror, you should not create the destination qtree. Thesnapmirror command automatically creates the destination qtree. So just volume creation of required size is good enough. Qtree SnapMirror determines changed data by first looking through the inode file for inodes that have changed and changed inodes of the interesting qtree for changed datablocks. The SnapMirror software then transfers only the new or changed data blocksfrom this Snapshot copy that is associated with the designated qtree. On the destinationvolume, a new Snapshot copy is then created that contains a complete point-in-timecopy of the entire destination volume, but that is associated specifically with theparticular qtree that has been replicated.

destination-filer> snapmirror initialize -S source-filer:/vol/demo1/qtreedestination-filer:/vol/demo1/qtree Transfer started. Monitor progress with 'snapmirror status' or the snapmirror log. 4) Monitoring the status : Snapmirror data transfer status can be monitored either fromsource or destination filer. Use "snapmirror status" to check the status.

destination-filer> snapmirror status Snapmirror is on. Source DestinationState Lag Status source-filer:demo_source destination-filer:demo_destinationUninitialized - Transferring (1690 MB done) source-filer:/vol/demo1/qtree destination-filer:/vol/demo1/qtreeUninitialized - Transferring (32 MB done) destination-filer>

5) Snapmirror schedule : This is the schedule used by the destination filer for updatingthe mirror. It informs the SnapMirror scheduler when transfers will be initiated. Theschedule field can either contain the word sync to specify synchronous mirroring or a cron-style specification of when to update the mirror. The cronstyle schedule contains four space-separated fields.

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If you want to sync the data on a scheduled frequency, you can set that in destination filer's /etc/snapmirror.conf . The time settings are similar to Unix cron. You can set a synchronoussnapmirror schedule in /etc/snapmirror.conf by adding sync instead of the cron stylefrequency.

destination-filer> rdfile /etc/snapmirror.conf source-filer:demo_source destination-filer:demo_destination - 0 * * *# This syncs every hour source-filer:/vol/demo1/qtree destination-filer:/vol/demo1/qtree - 0 21 * *# This syncs every 9:00 pm destination-filer>

6) Other Snapmirror commands

To break snapmirror relation - do snapmirror quiesce and snapmirror break. To update snapmirror data - do snapmirror update To resync a broken relation - do snapmirror resync.

To abort a relation - do snapmirror abortSnapmirror do provide multipath support. More than one physical path between a source and adestination system might be desired for a mirror relationship. Multipath support allows SnapMirror trafficto be load balanced between these paths and provides for failover in the event of a network outage.