VERITAS Volume Manager 3.5 User's Guide - VERITAS Enterprise Administrator (June 2002)

Chapter 4, Volume Tasks 99
Adding a Log to a Volume
Adding a Log to a Volume
The volume Add Log procedure adds the appropriate type of log to a mirroredor RAID-5
volume.
When usedto add aDirty Region Logging (DRL) log to amirroredvolume, DRL usesthis
log to track the regions of the volume that change due to I/O writes. If a system failure
occurs, DRL uses the information in the log to recover only the portions of the volume
that need recovery. This speeds up recovery time for mirrored volumes.
For DRL to be in effect, a mirrored volume must have at least one DRL log. You can create
additional DRL logs (on different disks) to mirror the DRL information.
When used toadd a logtoa RAID-5volume,the logspeedsup theresynchronizationtime
for RAID-5volumes after asystem failure. A RAID-5 log maintains a copy ofthe data and
parity being written to the volume atany given time. Ifa system failure occurs, VxVM can
“replay”the RAID-5 log toresynchronize the volume. This copiesthe data and parity that
was being writtenat the time offailurefromthe log to theappropriateareasof theRAID-5
volume. You can create multiple RAID-5 logs (on different disks) to mirror the log
information. Ideally, each RAID-5 volume has at least two logs.
1. Select the mirrored volume or RAID-5 volume to contain the log.
2. Select Actions > Log > Add.
3. By default the “Auto assign destination disks” option will be selected. To manually
assign the destination disks, select the “Manually assign destination disks” option.
Available disks will appear in the left window. To add destination disks, select them
in theleft window and click theAdd button. To addall of the availabledisks, click the
Add All button.
To remove destination disks, select them in the right window and then click the
Remove button. To remove all of the destination disks, click the Remove All button.
4. Click Apply to create the Log then OK.
Notes:
- When a log is added to a mirrored volume, DRL is activated for that volume.