VERITAS Volume Manager 3.5 Troubleshooting Guide (August 2002)

Recovery from DCO Volume Failure
16 VERITAS Volume Manager Troubleshooting Guide
Recovery from DCO Volume Failure
Persistent FastResync uses a data change object (DCO) log volume to perform tracking of
changed regions in a volume.If anerroroccurs whilereadingor writing a DCO volume,it
is detached and the badlog flag is set on the DCO. (You can use one of the options -a,
-F or -m to vxprint to check if the badlog flag is set on a DCO.) All further writes to
the volume are not tracked by the DCO.
To recover the DCO volume, perform the following steps:
1. Correct the problem that caused the I/O failure.
2. Use the following command to remove the badlog flag from the DCO:
# vxdco -g diskgroup -o force enable dco
3. Restart the DCO volume using the following command:
# vxvol -g diskgroup start dco_log_vol
4. Use the vxassist snapclear command to clear the FastResync maps for the
original volume and for all its snapshots. This ensures that potentially stale
FastResync maps are not used when the snapshots are snapped back (a full
resynchronization is performed). FastResync tracking is re-enabled for any
subsequent snapshots of the volume.
Caution You must use the vxassist snapclear command on all the snapshots of the
volume afterremoving the badlog flag from theDCO. Otherwise, data maybe
lost or corrupted when the snapshots are snapped back.
If a volume and its snapshot volume are in the same disk group, the following
command clears the FastResync maps for both volumes:
# vxassist -g diskgroup snapclear volume snap_obj_to_snapshot
Here snap_obj_to_snapshot is the name of the snap object associated with volume
that points to the snapshot volume.
If a snapshot volume and the original volume are in different disk groups, you must
perform a separate snapclear operation on each volume:
# vxassist -g diskgroup1 snapclear volume snap_obj_to_snapshot
# vxassist -g diskgroup2 snapclear snapvol snap_obj_to_volume
Heresnap_obj_to_volume is the name of the snapobject associated with the snapshot
volume, snapvol, that points to the original volume.