Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)

Note: The Disk Group Split/Join functionality is not used. As all processing takes
place in the same disk group, synchronization of the contents of the snapshots
from the original volumes is not usually required unless you want to prevent disk
contention. Snapshot creation and updating are practically instantaneous.
Figure 11-2 shows the suggested arrangement for implementing solutions where
the primary host is used and disk contention is to be avoided.
Figure 11-2
Example point-in-time copy solution on a primary host
Disks containing primary
volumes used to hold
production databases or file
systems
Disks containing synchronized
full-sized instant snapshot
volumes
Primary host
1 2
SCSI or Fibre
Channel connectivity
In this setup, it is recommended that separate paths (shown as 1 and 2) from
separate controllers be configured to the disks containing the primary volumes
and the snapshot volumes. This avoids contention for disk access, but the primary
host’s CPU, memory and I/O resources are more heavily utilized when the
processing application is run.
Note: For space-optimized or unsynchronized full-sized instant snapshots, it is
not possible to isolate the I/O pathways in this way. This is because such snapshots
only contain the contents of changed regions from the original volume. If
applications access data that remains in unchanged regions, this is read from the
original volume.
Implementing off-host point-in-time copy solutions
Figure 11-3 illustrates that, by accessing snapshot volumes from a lightly loaded
host (shown here as the OHP host), CPU- and I/O-intensive operations for online
127Understanding point-in-time copy methods
About point-in-time copies