HP StorageWorks XP Remote Web Console Software User Manual
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ShadowImage for the XP128/XP1024/XP10000/XP12000
When an SI390 volume pair is added, the data on the S-VOL is copied to the T-VOL. During this initial
copy operation and after the pair status becomes duplex, all write operations to the T-VOL are prohibited.
If you need to access a T-VOL, you can split the pair to make the T-VOL accessible (the S-VOL is always
accessible). While an SI390 pair is split, the XP128/XP1024/XP10000/XP12000 keeps track of all
changes to the S-VOL and T-VOL as a differential bitmap. When you resync the pair, the differential data in
the S-VOL (due to S-VOL and T-VOL updates) is copied to the T-VOL so that the T-VOL is again identical to
the S-VOL.
NOTE:
SI390 T-VOLs are updated asynchronously. For a volume pair with duplex status, the S-VOL and
T-VOL may not be identical. For more information on SI390 update copy operations, refer to ”
SI390 S-VOLs or T-VOLs should not be concentrated in the same RAID group. To disperse workloads of the
RAID groups, each RAID group should have both S-VOLs and T-VOLs evenly distributed. SI390 pairs for
which an SI390 operation is performed simultaneously should be in different RAID groups. If SI390 pairs
are concentrated in only a few RAID groups, the host I/O performance may be degraded. To minimize
effect on the host I/O performance, take the following actions:
•
Specify Slower for the copy pace when you create, split, or resync SI390 pairs.
•
If the SI390 pairs that you want to perform copy operation are in the same ECC group, reduce the
number of pairs at one copy operation. For example, to split multiple SI390 pairs in the same ECC
group, wait until one pair is completely split before splitting another pair.
If the XP128/XP1024/XP10000/XP12000 is overloaded, you must increase cache, disk adapters,
and/or RAID groups. Consider assigning SI390 T-VOLs in the newly installed RAID groups. If you continue
SI390 operations with an overloaded XP128/XP1024/XP10000/XP12000, host I/O performance may
be degraded.
Copy Threshold option: If the load of the disk array increases, host server I/O performance (response) may
be degraded. If ShadowImage for z/OS performs copy operations when the load of the disk array is
heavy, it is more likely that host server I/O performance (response) may be degraded. The Copy Threshold
option temporarily stops ShadowImage copy operations when the load of the disk array is heavy. If you set
this option in effect, you can minimize the degradation of host I/O performance by temporarily stopping
ShadowImage for z/OS copy operations when the load of the disk array is heavy.
ShadowImage for z/OS has another option called the Host I/O Performance option, which maintains host
I/O performance (response). Host I/O Performance option suppresses ShadowImage for z/OS copy
operation regardless of the status of the disk array. On the other hand, the Copy Threshold option is
effective only when the load of the disk array is heavy. When the Copy Threshold option is in effect, all the
ShadowImage for z/OS copy operations stop.
For information about the setting of the Host I/O Performance option, see
Host I/O Performance Option” on
. For information about the setting of the Copy Threshold option, please call the HP Account
Support Representative.
NOTE:
Copy operations that are stopped by the Copy Threshold option will resume when the load of the
disk array become light. If this option is in effect, not only ShadowImage for z/OS copy operation but also
the copy operations of the following program products will stop when the load of the disk array is heavy.
•
Business Copy XP
•
Hitachi FlashCopy Mirroring
•
Hitachi FlashCopy Mirroring Version 2
•
Snapshot XP
•
Flex Copy XO
•
Auto LUN XP