HP XP Business Copy Software - Manual (Page 12)

Figure 3 Update Copy Operation
CAUTION: Even if the copy operation is completed without any host I/O, the data in the S-VOL
and the data in the T-VOL may not be the same. Whether the S-VOL and the T-VOL have the same
data depends on the condition of the storage system. To make the S-VOL data and the T-VOL data
equal, split the pair and make the pair status split.
Update copy operations are not performed for SIz pairs with the following statuses: pending,
SP-pend, V-Split, split, resync, resync-R, and suspend.
Update copy operations do not occur every time a host issues a write I/O operation to the S-VOL
of a ShadowImage for Mainframe pair. SIz update copy operations are performed asynchronously
according to the differential bitmap, which is stored in shared memory.
If shared memory is lost (for example, offline micro exchange or volatile power supply on) the
differential bitmap is also lost. In this case, the XP24000/XP20000 disk array treats the entire
S-VOL (T-VOL for resync-R pairs) as difference data and recopies all data to the T-VOL (S-VOL for
resync-R pairs) to ensure proper pair resynchronization. For pairs in SP-pend or V-Split status, the
storage system changes the status to suspend due to the loss of the differential bitmap, ensuring
proper resynchronization of these pairs. If shared memory has been lost, extra time is required for
SIz operations since the XP24000/XP20000 disk array needs to copy the entire volume.
Split Pair Operation
The ShadowImage for Mainframe split capability provides point-in-time backup of your data, and
also facilitates real data testing by making the SIz copies (T-VOLs) available for host access. The
SIz split operation copies whole S-VOL data or differential data at that time to the T-VOL to make
the T-VOL identical to the state of the S-VOL when the split command was issued. If there are many
host I/Os for the S-VOL, it may take time to synchronize the S-VOL and the T-VOL. When the split
operation is complete, the pair status changes to split. Note that the split operations cannot be
performed on the pair whose status is suspend, resync or resync-R.
While the pair is split, the XP storage system establishes a differential bitmap for the split S-VOL
and T-VOL and records all updates to both volumes. The S-VOL remains fully accessible during the
split operation. Whether you can access the T-VOL depends on what split type is specified. There
are two kinds of split types, Quick Split and Steady Split. In addition to the split types, there is
At-Time Split which allows you to split all the pairs in the CTG. You can perform Quick Split and
12 About ShadowImage for Mainframe Operations