VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 1, Understanding VERITAS Volume Manager

SmartSync Recovery Accelerator

FastResync Limitations

The following limitations apply to FastResync:

◆ Persistent FastResync is supported for RAID-5 volumes, but this prevents the use of

the relayout or resize operations on the volume while a DCO is associated with it.

◆ Neither Non-Persistent nor Persistent FastResync can be used to resynchronize

mirrors after a system crash. Dirty region logging (DRL), which can coexist with

FastResync, should be used for this purpose.

◆ When a subdisk is relocated, the entire plex is marked “dirty” and a full

resynchronization becomes necessary.

◆ If a snapshot volume is split off into another disk group, Non-Persistent FastResync

cannot be used to resynchronize the snapshot plexes with the original volume when

the disk group is rejoined with the original volume’s disk group. Persistent

FastResync must be used for this purpose.

◆ If you move or split an original volume (on which Persistent FastResync is enabled)

into another disk group, and then move or join it to a snapshot volume’s disk group,

you cannot use vxassist snapback to resynchronize snapshot plexes with the

original volume. This restriction arises because a snapshot volume references the

original volume by its record ID at the time that the snapshot volume was created.

Moving theoriginal volumeto a differentdisk group changesthe volume’srecordID,

and so breaks the association. However, in such a case, you can use the vxplex

snapback command with the -f (force) option to perform the snapback.

◆ Any operation that changes the layout of a replica volume can mark the FastResync

change map for that snapshot “dirty” and require a full resynchronization during

snapback. Operations that cause this include subdisk split, subdisk move, and online

relayout of the replica. It is safe to perform these operations after the snapshot is

completed. For more information, see the vxvol (1M), vxassist (1M), and vxplex

(1M) manual pages.

SmartSync Recovery Accelerator

TheSmartSync feature of VERITASVolume Manager increasestheavailability of mirrored

volumesby only resynchronizingchangeddata. (The processof resynchronizingmirrored

databases is also sometimes referred to as resilvering.) SmartSync reduces the time

required to restore consistency, freeing more I/O bandwidth for business-critical

applications. The SmartSync feature uses an extended interface between VxVM volumes

and the database software to avoid unnecessary work during mirror resynchronization.

For example, Oracle

automatically takes advantage of SmartSync to perform database

resynchronization when it is available.