Enabling FastResync on a Volume

FastResync performs quick and efficient resynchronization of stale mirrors. It also increases the efficiency of the VxVM snapshot mechanism when used with operations such as backup and decision support. See Administering Volume Snapshots and FastResync for more information.

There are two possible versions of FastResync that can be enabled on a volume:

• Persistent FastResync holds copies of the FastResync maps on disk. These can be used for the speedy recovery of mirrored volumes if a system is rebooted. This form of FastResync requires that either a version 0 or a version 20 data change object (DCO) and DCO volume first be associated with the volume.

See Adding a Version 0 DCO and DCO Volume, and Preparing a Volume for DRL and Instant Snapshots for more information on version 0 and version 20 DCO volumes respectively.

If the existing volume was created in a previous release of VxVM, and it has any attached snapshot plexes or it is associated with any snapshot volumes, follow the procedure given in Upgrading Existing Volumes to Use Version 20 DCOs.

• Non-Persistent FastResync holds the FastResync maps in memory. These do not survive on a system that is rebooted.

By default, FastResync is not enabled on newly created volumes. Specify the fastresync=on attribute to the vxassist make command if you want to enable FastResync on a volume that you are creating.

To turn FastResync on for an existing volume, specify fastresync=on to the vxvol command as shown here:

Checking Whether FastResync is Enabled on a Volume

To check whether FastResync is enabled on a volume, use the following command:

This command returns on if FastResync is enabled; otherwise, it returns off.

If FastResync is enabled, to check whether it is Non-Persistent or Persistent FastResync, use the following command:

This command returns on if Persistent FastResync is enabled; otherwise, it returns off.

To list all volumes on which Non-Persistent FastResync is enabled, use the following command:

To list all volumes on which Persistent FastResync is enabled, use the following command:

Disabling FastResync

Use the vxvol command to turn off Persistent or Non-Persistent FastResync for an existing volume, as shown here:

Turning FastResync off releases all tracking maps for the specified volume. All subsequent reattaches will not use the FastResync facility, but perform a full resynchronization of the volume. This occurs even if FastResync is later turned on.