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Using Veritas Volume Manager FastResync

FastResync (FR) enables you to split off a plex from a mirrored volume, manipulate it, and then reattach it to the original volume without doing a complete resynchronization of the volume. FastResync is a separately licensed feature of VxVM.

FR maintains a bitmap of changes to the volume while the plex was split off, and also of changes to the split-off mirror. When the plex is attached, only the blocks represented in the map are resynchronized.

You can use FR to perform the snapback operation after the off-host processing operation is complete.

The operations performed by the vxrvg snapshot and vxrvg snapback commands are based on one of the following conditions:

• If you do not have an FR license, the vxrvg snapshot command creates a simple snapshot without any FR bitmaps. A vxrvg snapback operation then results in a full resynchronization of the plexes.
• If you have an FR license and FastResync is enabled on the volumes, but no DCO logs are attached to the data volumes, the vxrvg snapshot command creates a snapshot with a non-persistent FR bitmap. A vxrvg snapback operation performs a FastResync, but if the system reboots at any time after the snapshot operation, the information in the FR bitmap is lost and a full resynchronization takes place.
• If you have an FR license, FastResync is enabled, and DCO logs are attached to the data volumes, the vxrvg snapshot command creates a snapshot with persistent FR bitmap. A vxrvg snapback operation performs a FastResync even if the system reboots at any point in time after the snapshot operation.

For more information on Persistent and Non-Persistent FR, see the Veritas Volume Manager Administrator's Guide.

Enabling FastResync

To enable FR on a data volume, type:

# vxvol -g diskgroup set fmr=on dv_name

Do this for all the data volumes in the RVG that you want to access.

Refer to the Veritas Volume Manager Administrator's Guide for more information.