SnapMirror support for NetApp snapshot-assisted progressive incremental backup (snapdiff)

Scenario: Back up data on a source filer volume

You can configure the backup archive client to back up data from the source filer volumes. This scenario requires you to configure a Tivoli Storage Manager backup-archive client node such that it has access to the NetApp source filer volumes by using NFS-exported shares to mount the filer volumes.

You can configure the backup archive client to back up data from the source filer volumes. This scenario requires you to configure a Tivoli Storage Manager backup-archive client node such that it has access to the NetApp source filer volumes by using CIFS shares to mount the filer volumes.

For example, assume a configuration where the source filer is named ProdFiler. Assume that a volume named UserDataVol exists on ProdFiler filer and that the volume is accessible by using NFS from a backup-archive client node. Assume that the share is mounted as UserDataVol_Share.

For example, assume a configuration where the source filer is named ProdFiler. Assume that a volume named UserDataVol exists on ProdFiler filer and that the volume is accessible by using CIFS from a backup-archive client node. Assume that the share is mounted as UserDataVol_Share.

When you initiate a snapshot differential backup, the NetApp filer creates a new differential snapshot on the volume that is being backed up. That differential snapshot is compared with the base (previous) snapshot. The base snapshot name was registered on the Tivoli Storage Manager server when the previous backup was completed. The contents of that base snapshot are compared to the differential snapshot that is created on the source filer volume. Differences between the two snapshots are backed up to the Tivoli Storage Manager server.

dsmc incr \\ProdFiler\UserDataVol_Share -snapdiff -diffsnapshot=create

Back up data on a destination filer

A more typical configuration is to offload the backups from the source filer by creating backups of the source volumes by using the replicated volume snapshots stored on the destination filer. Ordinarily, backing up a destination filer presents a problem because creating a snapshot differential backup requires that a new snapshot must be created on the volume that you are backing up. The destination filer volumes that mirror the contents of the source volumes are read only volumes, so snapshots cannot be created on them.

To overcome this read-only restriction, Tivoli Storage Manager provides client configuration options that allow you to use the existing base and differential snapshots on the read-only destination volume to back up changes to the Tivoli Storage Manager server.

Like in the source filer scenario, the destination filer volumes are accessed by using NFS-exported shares.

Like in the source filer scenario, the destination filer volumes are accessed by using CIFS shares.

Snapshot differential options summary

If this option is not specified, a new snapshot is created on the volume that is being backed up. Because destination filer volumes are read-only volumes, useexistingbase must be specified when creating snapshot differential backups of destination filer volumes. If useexistingbase is not specified, snapshot differential backups of a destination filer volume fail because the new snapshot cannot be created on the read-only volume.

When backing up destination filer volumes, use both the useexistingbase option and the diffsnapshot=latest option to ensure that the most recent base and most recent differential snapshots are used during the volume backup.

You use the basesnapshotname option to specify which snapshot, on the destination filer volume, to use as the base snapshot. If you do not specify this option, the most recent snapshot on the destination filer volume is used as the base snapshot. You can use wildcards to specify the name of the base snapshot.

You use the diffsnapshotname option to specify which differential snapshot, on the destination filer volume, to use during a snapshot differential backup. This option is only specified if you also specify diffsnapshot=latest. You can use wildcards to specify the name of the differential snapshot.

The diffsnapshot=latest option specifies that you want to use the latest snapshot that is found on the file server as the source snapshot.

Additional information about each of these options is provided in the Client options reference topics.

Snapshot differential backup command examples

In the examples that follow, assume that volumes on a source filer are replicated, by using NetApp’s SnapMirror technology, to a disaster recovery filer (host name is DRFiler). Because the DRFiler volumes are read only, you use the options to specify which of the replicated snapshots that you want to use as the base snapshot, and which of the snapshots you want to use as the differential snapshot. By specifying the snapshots to use when creating a snapshot differential backup of a destination filer, no attempt is made to create a snapshot on the read-only volumes.

The following commands are used to initiate snapshot differential backups. Most of these commands create snapshot differential backups by using snapshots stored on the destination filer volumes. When backing up from a destination filer volume, be sure to include the -useexistingbase option, because that option prevents attempts to create a new snapshot on the read-only destination filer volumes.

Example 1: Back up a destination filer by using default nightly backups that were created by the NetApp snapshot scheduler

dsmc incr \\DRFiler\UserDataVol_Share -snapdiff -useexistingbase 
  -diffsnappshot=latest -basesnapshotname=”nightly.?”

You can use a question mark (?) to match a single character. In this example, -basesnapshotname=nightly.? uses the latest base snapshot that is named "nightly.", followed by a single character (for example: nightly.0, nightly.1, and so on).

Example 2. Back up a destination filer volume by using snapshots created manually (not created by the NetApp snapshot scheduler)

dsmc incr \\DRFiler\UserDataVol_Share –snapdiff –useexistingbase 
  –diffsnapshot=latest –basesnapshotname=”share_vol_base?” 
  –diffsnapshotname=”share_vol_diff?”

This example also uses the question mark (?) wildcard to illustrate the syntax if the base and differential snapshot names have different numbers as part of the name.

Example 3. Back up a destination filer volume, and specify which snapshots to use for the base and differential snapshots

dsmc incr \\DRFiler\UserDataVol_Share -snapdiff -useexistingbase 
  -diffsnapshot=latest -basesnapshotname=”share_vol_base” 
  –diffsnapshotname=”share_vol_diff_snap”

Example 4: Back up script-generated snapshots that use a naming convention

In this example, a script that is running on the NetApp filer adds a date and time stamp to the snapshot names. For example, a snapshot created on November 3, 2012 at 11:36:33 PM is named UserDataVol_20121103233633_snapshot. You can use wildcards with the options to select the most recent base and differential snapshots. For example:

dsmc incr \\DRFiler\UserDataVol_Share -snapdiff -useexistingbase 
  -basesnapshotname=”UserDataVol_Share_*_snapshot” –diffsnapshot=latest 
  -diffnsnapshotname=”UserDataVol_Share_*snapshot 

-useexistingbase selects the most recent base snapshot. Adding an asterisk (*) wildcard to -basesnapshotname selects the most recent base snapshot that follows the script-naming convention. The -diffsnapshot=latest option suppresses the creating of a new differential snapshot and -diffsnapshotname= selects the most recent existing differential snapshot that follows the script-naming convention. (The asterisks wildcards match any string).

Example 5: Perform a snapshot differential backup by using an existing differential snapshot that exists on the source filer

To use an existing differential snapshot that exists on the source filer, use the -diffsnapshot=latest to prevent the creation of a new differential snapshot. Also use the -diffsnapshotname option to specify which existing differential snapshot to use. The snapshot you specify is compared to the base snapshot, which was registered in the Tivoli Storage Manager server database when the last backup was created. For example:

dsmc incr \\ProdFiler\UserDataVol_Share -snapdiff -diffsnapshot=latest 
  -diffsnapshotname=”share_vol_diff_snap”