Veritas Storage Foundation 5.0.1 Cluster File System Administrator's Guide Extracts for the HP Serviceguard Storage Management Suite on HP-UX 11i v3

Performance Considerations
Mounting a snapshot file system for backup increases the load on the system because of the
resources used to perform copy-on-writes and to read data blocks from the snapshot. In this
situation, cluster snapshots can be used to do off-host backups. Off-host backups reduce the load
of a backup application on the primary server. Overhead from remote snapshots is small when
compared to overall snapshot overhead. Running a backup application by mounting a snapshot
from a lightly loaded node is beneficial to overall cluster performance.
Creating a Snapshot on a Cluster File System
The following example shows how to create and mount a snapshot on a two-node cluster using
CFS administrative interface commands.
1. Create a VxFS file system on a shared VxVM volume:
# mkfs –F vxfs /dev/vx/rdsk/cfsdg/vol1
version 7 layout 104857600 sectors, 52428800 blocks of size 1024,
log size 16384 blocks unlimited inodes, largefiles not supported
52428800 data blocks, 52399152 free data blocks 1600 allocation
units of 32768 blocks, 32768 data blocks
2. Mount the file system on all nodes (following previous examples, on system01 and
system02):
# cfsmntadm add cfsdg vol1 /mnt1 all=cluster
# cfsmount /mnt1
The cfsmntadm command adds an entry to the cluster manager configuration, then the
cfsmount command mounts the file system on all nodes.
3. Add the snapshot on a previously created volume (snapvol in this example) to the cluster
manager configuration:
# cfsmntadm add snapshot cfsdg snapvol /mnt1 /mnt1snap \ system01=ro
NOTE: The snapshot of a cluster file system is accessible only on the node where it is
created; the snapshot file system itself cannot be cluster mounted.
4. Mount the snapshot:
# cfsmount /mnt1snap
5. A snapped file system cannot be unmounted until all of its snapshots are unmounted.
Unmount the snapshot before trying to unmount the snapped cluster file system:
# cfsumount /mnt1snap
28 Cluster File System Administration