HP StorageWorks XP Remote Web Console Software - Manual (Page 46)

For example, assigning three S-VOLs to each P-VOL takes more resources than assigning only one
or two. The more S-VOLs you assign to a given P-VOL, the larger the attenuating effect on the
potential P-VOL I/O performance.
Note that when you assign only one S-VOL on a P-VOL, the pace of the initial copy operations
may affect the I/O performance of the storage system. Using a slower copy pace minimizes the
impact of Business Copy operations on I/O performance, while a faster copy pace produces
copies more quickly but may affect I/O performance.
• Load sharing of parity groups:
Business Copy P-VOLs or S-VOLs should not be concentrated in the same parity group. To disperse
workloads of the parity groups, P-VOLs and S-VOLs should be evenly distributed across parity
groups. Business Copy pairs for which Business Copy operations are performed simultaneously
should be in different parity groups. If Business Copy pairs are concentrated in only a few
parity groups, the host I/O performance may be degraded. To minimize the effect on the host
I/O performance, take the following actions:
• Specify
Slower for the copy pace when you create, split, or resynchronize Business Copy pairs.
• To perform copy operations on Business Copy pairs that are in the same parity group, reduce
the number of pairs at one copy operation. For example, to split multiple Business Copy pairs
in the same parity group, wait until one pair is completely split before splitting another pair.
If the storage system is overloaded, you must increase cache, disk adapters, and/or parity
groups. It is recommended that Business Copy S-VOLs be assigned in newly installed parity
groups. If you continue Business Copy operations with an overloaded storage system, host I/O
performance may be degraded. If the storage system is overloaded, consult HP technical support.
• Structure for the case using multiple program products at the same time:
If you are using more than one storage system data management program product (for example,
Business Copy, Continuous Access, Open Volume Management, Cache Residency Manager) at
the same time in the same storage system, contact HP technical support to ensure that your storage
system is optimized for your configuration of concurrent operations (for example, sufficient cache).
Each storage system program product can affect the performance of the storage system
and/or the operation of other program products. For example, Business Copy and Continuous
Access operations both involve initial copy operations and update copy operations to the
secondary/remote volumes in addition to the host I/O workload.
• Structure for AIX host servers:
When you use Business Copy on the AIX host servers, it is strongly recommended that you use
two AIX host servers to locate P-VOLs in one host server, and the paired S-VOLs in the other. If you
use only one AIX host server, keep in mind the following points:
• When the paircreate or pairresync operation is performed, Business Copy copying takes place
between the P-VOL and S-VOL, and consequently the P-VOL and S-VOL have the same PVID.
• If the host server reboots while the P-VOL and S-VOL have the same PVID, the host server might
misidentify the P-VOL and S-VOL (that is, identify the S-VOL as the P-VOL) after rebooting.
• You can use the recreatevg command to change the PVID of the P-VOL and S-VOL. However,
until the recreatevg command is executed, the PVID remains the same, and the host server
might misidentify the volumes.
• When you resynchronize a pair by Quick Restore:
During a quick restore operation, the RAID levels, HDD types, and Cache Residency Manager
settings of the P-VOL and S-VOL are exchanged. For example, if the P-VOL has a RAID-1 level
and the S-VOL has a RAID-5 level, the quick restore operation changes the RAID level of the
P-VOL to RAID-5 and of the S-VOL to RAID-1. This also applies to RAID-6 volumes. To avoid any
performance impact due to the quick restore operation:
• Make sure that the P-VOL and S-VOL have the same RAID level and HDD type before
performing the quick restore operation. To restore the original RAID levels after quick restore,
stop host I/Os to the pair, split the pair, perform the quick restore operation for that pair
again, and then restart the host I/Os to the pair.
• Because the Cache Residency Manager settings are exchanged during a quick restore
operation, you must perform one of the two following operations:
• Set the same Cache Residency Manager settings (locations) for the P-VOL and S-VOL
before performing the quick restore operation.
46 Preparing for Business Copy Operations