HP StorageWorks XP Remote Web Console Software - Manual (Page 18)

Host
Storage Navigator Computer
(Web Client)
Storage Navigator
Java applet
Tagmastore TM USP/NSC
storage system
Download
SVP
(Web Server)
S-VOL
Copy
T-VOL
T-VOL
T-VOL
ShadowImage for
z/OS ® pair
Figure 1 Hitachi ShadowImage for zOS configuration
Volume Pairs (S-VOLs and T-VOLs)
The storage system contains and manages both the original and copied Siz data. Siz supports a
maximum of 16,384 pairs (8,192 pairs: 8,192 S-VOLs and 8,192 T-VOLs).
Siz performs internal copy operations for logical volume pairs established by the user. Each Siz pair
consists of one source volume (S-VOL) and up to three target volumes (T-VOLs) which are located in the
same storage system. The Siz S-VOLs are the source volumes which contain the original data. The Siz
T-VOLs are the target or secondary (mirrored) volumes which contain the backup data. Each T-VOL
must be paired with only one S-VOL.
During normal Siz operations, the S-VOLs remain available to all hosts at all times for read and write I/O
operations. The T-VOLs become available for host access only after a split operation has been performed.
When a Siz 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 a Siz pair is split, the storage system 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.
Siz T-VOLs are updated asynchronously. For a volume pair with duplex status, the S-VOL and
T-VOL may not be identical. For further information on Siz update copy operations, see section
“ Add Pair Operation ” on page 26.
Siz 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. Siz pairs for
which a Siz operation is performed simultaneously should be in different RAID groups. If Siz 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 Siz pairs.
18 Overview of Hitachi ShadowImage for z/OS Operations