HP StorageWorks XP Business Copy Software user guide: HP XP12000 Disk Array, HP XP10000 Disk Array, HP 200 Storage Virtualization System (T1713-96027, April 2010)

or mirrored volumes containing backup data. Each S-VOL must be paired with only one P-VOL. During
BC operations, P-VOLs remain available to all hosts for read and write I/O operations (except during
reverse resync and quick restore). S-VOLs become available for host access only after the pair is split.
When a BC volume pair is created, data on the P-VOL is copied to the S-VOL to synchronize the
volumes. During this initial copy operation and after the pair is synchronized, all write operations to
the S-VOL are prohibited. To access an S-VOL, you can “split” the pair to make the S-VOL accessible.
While a BC pair is split, the disk array keeps track of all changes to the P-VOL and S-VOL. When you
“resync” the pair, the differential data in the P-VOL (due to P-VOL and S-VOL updates) is copied to
the S-VOL, so the S-VOL is again identical to the P-VOL. For reverse resync, the differential data in
the S-VOL (due to P-VOL and S-VOL updates) is copied to the P-VOL, so the P-VOL is now identical to
the S-VOL.
NOTE:
BC S-VOLs are updated asynchronously. For a volume pair with PAIR status, the P-VOL and S-VOL
may not be identical. For further information on BC update copy operations, see Paircreate operation.
BC P-VOLs or S-VOLs should not be concentrated in the same RAID group. To disperse workloads of
RAID groups, each RAID group should have both P-VOLs and S-VOLs evenly distributed. BC pairs
for which BC operations are performed simultaneously should be in different RAID groups. If BC pairs
are concentrated in only a few RAID groups, host I/O performance may be degraded.
If the disk array is overloaded, increase cache, disk adapters, and/or RAID groups. Consider assigning
BC S-VOLs in newly installed RAID groups. If you continue BC operations with an overloaded disk
array, host I/O performance may be degraded.
Copy Threshold option
If BC performs copy operations when the disk array workload is heavy, host server I/O performance
might be degraded. To minimize this performance degradation, enable Copy Threshold, which
temporarily stops all BC copy operations when the disk array has a heavy workload. Copy operations
that are stopped by the Copy Threshold option resume when the disk array workload is lighter.
This option is different from the Host I/O Performance option (Host I/O Performance option), because
it is effective only when the disk array workload is heavy.
NOTE:
Contact your HP support account representative for more information about the Copy Threshold
option.
In addition to BC operations, Copy Threshold temporarily stops copy operations for the following
applications when the disk array workload is heavy:
• Auto LUN XP
• ShadowImage for z/OS
• Hitachi FlashCopy Mirroring
• Hitachi FlashCopy Mirroring Version 2
• Snapshot XP
• Flex Copy XP
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