Understanding Volume Replicator support for FlashSnap

The FlashSnap feature available with Storage Foundation enables you to perform off-host operations on volumes by creating independent mirrors of volumes on the server.

FlashSnap comprises of a multi-step process that can include the following operations:


Creates a snapshot mirror of the volumes.

The Prepare command replaces the Snap Start command in the GUI. Both prepare and snapstart keywords are available in the CLI, however prepare is the recommended keyword.


Create snapshot volumes by breaking off the mirrors.

Disk group split

Forms a new disk group using these snapshot volumes which can be used for off-host processing.

For detailed steps on creating the snapshots for off-host processing, refer to the steps that are described in the section "Off-Host FlashSnap Procedure (Two Servers)" in the Storage Foundation Administrator's Guide.


For creating a snapshot, you must use the vxrvg snapshot without the -f option to create disk group split friendly snapshots.

Disk group join

Joins the new disk group back to the original disk group once the off-host processing is done.


Reattaches the snapshot volumes back to the original volume.


A valid license for Storage Foundation FlashSnap feature must be present on all the systems on which you want to use the snapshot operations.

For more information about the FlashSnap feature refer to the Storage Foundation Administrator's Guide.

The need for Volume Replicator to support FlashSnap arises from the fact that if the snapshot volume is created on a disk that is a part of an RVG, then, splitting the disk group with this snapshot volume is not allowed as it breaks the Volume Replicator configuration.

Now as a part of the FlashSnap support, Volume Replicator supports RVG-wide snapshot and snapback operations. This can be performed on the Primary as well as the Secondary RVGs in an RDS. Volume Replicator ensures that only disk group split-friendly snapshots are created.

Figure: Working of the snapshot and snapback operations

Working of the snapshot and snapback operations

The data in the original volume may change, however, the snapshot can still be used as a stable and independent copy for various purposes. The snapshots can be used as backup copies to restore the data that may have been lost due to disk failure, software, or human errors. You can perform system backup, upgrade, and other maintenance tasks on point-in-time copies, while providing continuous availability of your critical data. A volume snapshot is also used to execute offline backups without affecting the application performance. They can also be used for restoring data both on the Primary and Secondary, if the original data gets corrupted due to logical or media errors. The snapshot volumes can be replicated and can also be included as a part of the RVG.


While the snapshot volume is a part of the RVG it cannot be used for recovery as a consistent point-in-time copy of the data.

Another important advantage of the Volume Replicator snapshot operation is that it supports an RVG friendly disk group split operation. It ensures that the resultant snapshot volume lie on the disks that are not under an RVG, that is, the disks that do not contain any plex of a replicated volume. Thus, a disk group split operation on the snapshot volume(s) keeps the existing Volume Replicator configuration intact and does not fail because the Volume Replicator configuration was disturbed.


If the snapshot volumes lie on disks within an RVG, the Volume Replicator snapshot operation fails, provided the force option is not used.

For example, consider the following scenario:

A disk group dg1 has two disks disk1 and disk2. An RVG with two data volumes and a Replicator Log is created in this disk group. Both the data volumes reside on disk1 while the Replicator Log is on disk2. The two data volumes are prepared and the prepared plexes lie on disk2. In this scenario the Volume Replicator snapshots fails (provided force option has not been used) because the disk2 on which the snapshot volumes need to be created is a part of an RVG, as it contains the Replicator Log of the RVG.

More Information

Conditions for creating disk group split friendly snapshots