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

FastResync
48 VERITAS Volume Manager Administrator’s Guide
To snapshot all the volumes in a single disk group, specify the option -o allvols to
vxassist. However, this fails if any of the volumes in the disk group do not have a
complete snapshot plex.
It isalso possible to take several snapshotsof the same volume. A newFastResync change
map isproduced foreach snapshot taken tominimize the resynchronization timefor each
snapshot.
By default, the snapshot plex is resynchronized from the data in the original volume
during a snapback operation. Alternatively, you can choose the snapshot plex as the
preferred copy of the data when performing a snapback as illustrated in
“Resynchronizing the Original Volume from the Snapshot.” Specifying the option -o
resyncfromreplica to vxassist resynchronizes theoriginal volume from the data in
the snapshot.
Resynchronizing the Original Volume from the Snapshot
Note The original volumemust not be in use during asnapback operation that specifies
the option-o resyncfromreplica to resynchronize the volumefrom a snapshot.
Stop any application, such as a database, and unmount any file systems that are
configured to use the volume.
It is possible to grow the replica volume, or the original volume, and still use FastResync.
Growing the volume extends the map that FastResync uses to track changes to the
original volume. This can change either the size of the map, or the size of the region
represented by each bit in the map. 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
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.
Original
volume
snapshot
Snapshot
volume
Snapshot
mirror
-o resyncfromreplica snapback
Refresh on
snapback