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Instant plex-breakoff snapshots

The vxrvg snapshot command creates instant plex-breakoff snapshots of all the volumes in the RVG at a single point in time.

The steps required to create plex-breakoff snapshots are as follows:

• Preparing the RVG volumes for snapshot operation
• Creating snapshot plexes for Data Volumes in an RVG
• Freezing or Pausing Replication
• Creating an instant plex-breakoff snapshot
• Unfreezing or Resuming Replication

Preparing the RVG volumes for snapshot operation

It is necessary to prepare the volumes under the RVG for the snapshot operation. For more information on preparing volumes, refer to Preparing the volumes.

Creating snapshot plexes for data volumes in an RVG

You must create plexes for the required volumes before you take an instant plex breakoff snapshot.

Use the vxsnap addmir command to add one or more plexes to a volume:

# vxsnap -g diskgroup [-b] addmir volume [nmirror=<N>] \
[attributes...]

  Note   Run this command on every data volume in the RVG that needs the plex-breakoff snapshot to be created.

For more information on creating the plexes, refer to the Veritas Volume Manager Administrator's Guide.

Freezing or pausing replication

For more information on freezing or pausing the replication, refer to Freezing or pausing replication.

Creating instant plex breakoff snapshots

The instant plex-breakoff snapshot feature enables you to create plex-breakoff snapshots just like the traditional snapshot feature. This operation cannot be used for an RVG that consists of VxVM ISP volumes.

Prerequisites for creating instant plex breakoff snapshots

  Make sure the volumes for which you want to create plex-breakoff snapshots already have the appropriate plexes created and are in an snapdone state.

  Make sure you create the plexes using appropriate prefixes in case you want to use specific plexes for the snapshot operation.
For example, <plexprefix>-<volume_name>

  Note   If you do not specify the plexprefix attribute when creating the plex-breakoff snapshots, a plex that is in the snapdone state gets selected, automatically.

To create a plex-breakoff snapshot of each data volume in an RVG, use the following command: 

# vxrvg -g diskgroup [-P prefix] snapshot rvg_name \

[instantfull=volume_list [syncing=yes|no]] \

[instantso=volume_list {cache=cachename|cachesize=size}] \

[exclude=volume_list] [plexprefix=plex_prefix] \

[comment="<comment>"]

Use the vxrvg snapshot command with its attributes to specify the type of snapshot that you want to create. This is the default if neither the -S nor the -F option is specified. By default, all the volumes will be included for instant plex breakoff snapshots, provided that they have the plex volumes appropriately created. To exclude any of the volumes, use one of the following attributes. Depending on the attribute specified with the vxrvg snapshot command, appropriate snapshots of the volumes are created.

The attribute exclude specifies a comma-separated list of volumes that do not need to be considered for any kind of snapshot.

The plexprefix attribute specifies a prefix for the plexes that will be used for creating the plex-breakoff snapshots. This is allowed only if the -F or -S option is not specified or if you have specified a list of volumes for creating plex-breakoff volumes with the vxrvg snapshot command.

Example:

This example describes the steps to create an instant plex breakoff snapshot for an RVG:

1. Prepare the required volumes if they have not been prepared already.

   # vxsnap -g hrdg prepare hr_dv01

2. If the volumes for which the plex-breakoff snapshots need to be created do not have the required plexes, create them using the following command:

   # vxsnap -g hrdg addmir hr_dv01

   Repeat this step for all the required data volumes in the RVG. Initial synchronizing of the plexes may take some time depending on the size of the volume.

   If you need to use specific plexes during the snapshot operation, make sure you name them appropriately when creating them. However, you can also do it later using the following command:

   # vxedit -g hrdg rename hr_dv01-02 snapplex-dv01

3. Use the following command to create snapshots using the specific plex prefixes:

   # vxrvg -g hrdg -P JULY snapshot hr_rvg plexprefix=snapplex

   Use the following command to create the snapshots without specifying the plex prefix:

   # vxrvg -g hrdg -P JULY1 snapshot hr_rvg

Unfreezing or resuming replication

After taking a snapshot, unfreeze replication if you are using IBC messaging; otherwise, if you have paused replication, resume it. The snapshots are now ready for use.