VERITAS Storage Foundation 4.1 Cluster File System HP Serviceguard Storage Management Suite Extracts, December 2005

Snapshots on CFS
80 Installation and Administration Guide
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 from the primary server. Overhead from remote
snapshots is small when compared to overall snapshot overhead. Therefore, running a
backup application by mounting a snapshot from a relatively less 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.
▼ To create a snapshot on a cluster file system
1. Create a VxFS file system on a shared VxVM volume:
# mkfs –F vxfs /dev/vx/rdsk/cfsdg/vol1
version 4 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.