Hitachi ShadowImage for IBM z/OS User"s Guide (T5213-96002, June 2007)

Preparing for ShadowImage™ for IBM
®
z/OS
®
3-5
Hitachi ShadowImage™ for IBM
®
z/OS
®
User’s Guide
Assessing ShadowImage for z/OS Requirements
This section describes the assessments about SIz operations, such as how
many pairs you are going to create or how to decide the settings like copy
pace and paths.
Calculating Maximum Number of Pairs
When you create SIz pairs, resources called differential tables and pair tables
will be required. The number of available differential tables and pair tables in
one storage system depends on whether the additional shared memory is
installed or not. There are several patterns of additional shared memory for
differential tables and pair tables, and you can choose any pattern you like.
Table 3-2 shows the pattern of additional shared memory.
Table 3-2 Additional Shared Memory for Differential Tables
Additional Shared Memory for
SIz
Num. of Differential
Tables
Num. of Pair Tables Num. of Volumes in
Storage System
No additional shared memory for
SIz
0 0 1,024
Additional shared memory for
SIz is installed
26,176 8,192 16,384
Extension 1 57,600 8,192 16,384
Extension 2 104,768 16,384 65,536
Extension 3 146,688 16,384 131,072
Extension 4 209,600 16,384 131,072
Note:
– To install additional shared memory for differential tables, please call
the Support Center.
– Even if you install additional shared memory for differential tables and
pair tables, the maximum number of pairs is half of the total number of
volumes in the storage system (see Table 3-2). For example, if
additional shared memory for SIz is installed (second line in Table 3-2),
and when S-VOLs and T-VOLs are in a one-to-one relationship, you can
create up to 8,192 pairs. However, note that in case of Extension 2 to
Extension 4, the maximum number of pairs is 16,384 regardless of the
total number of volumes in the storage system.
To calculate the maximum number of SIz pairs, first you need to calculate how
many differential tables and pair tables are required to create SIz pairs, and
then compare the result with the number of differential tables and pair tables
in the whole storage system. Note that in addition to ShadowImage for z/OS,
the following program products will also use differential tables and pair tables.
• Program products using differential tables