Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 1, Understanding VERITAS Volume Manager

FastResync

In either case, the part of the map that corresponds to the grown area of the volume is

marked as “dirty” so that this area is resynchronized. The snapback operation fails if it

attempts to create an incomplete snapshot plex. In such cases, you must grow the replica

volume, or the original volume, before invoking any of the commands vxsnap

reattach, vxsnap restore, or vxassist snapback. Growing the two volumes

separately can lead to a snapshot that shares physical disks with another mirror in the

volume. To prevent this, grow the volume after the snapback command is complete.

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. In VxVM 4.0 and later releases, DRL logs

may be stored in a version 20 DCO volume.

◆ 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 traditional 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 the original volume to a different disk group changes the volume’s record ID,

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.

Note This restriction only applies to traditional snapshots. It does not apply to instant

snapshots.

◆ 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.