Hitachi TrueCopy for IBM z/OS User and Reference Guide (T5211-96001, June 2007)

3-10 Preparing for TrueCopy for z/OS Operations
Hitachi Universal Storage Platform V TrueCopy for IBM z/OS User’s Guide
Assessing TCz Requirements
Calculation of the Maximum Number of Pairs
The differential data (updated by write I/Os during suspension) between M-
VOL and R-VOL is stored in each track bitmap. When a released/suspended
pair is resynchronized, the MCU merges the M-VOL and R-VOL bitmaps, and
the differential data is copied to the R-VOL.
The maximum number of pairs you can create is restricted. Use the number of
cylinders and bitmap areas to calculate the maximum number of pairs that can
be created in a storage system.
• The number of cylinders:
The number of cylinders depends on the capacity of the volumes (the
number of cylinders set by VLL, if you set the VLL feature) used for the
pairs. Both the MCU and RCU are restricted.
• The number of bitmap areas:
To calculate the number of bitmap areas in each volume:
The number of bitmap areas = ( ↑ ((Number of cylinders × 15) /
122,752) ↑ )
The ↑…↑ symbols around a value indicate that the value should be rounded up to the next integer.
Note: 122,752 is the amount of differential data per bitmap area. The unit
for the amount of differential data is bits.
• The maximum number of pairs that can be created:
The number of bitmap areas you can use in storage system depends on the
number of shared memories you add to storage system. Table 3-1 shows
the relation between the number of shared memories and the number of
usable bitmap areas of storage system.
Table 3-1 Relation between the Additional Shared Memory and the
Number of Usable Bitmap Areas of Storage System
Additional Shared Memory for TCz Number of Usable Bitmap Areas of Storage System
No additional shared memory for TCz 0
Additional shared memory for TCz is
installed
7,424
Extension 1 16,384
Extension 2 32,768
Extension 3 44,256
Extension 4 65,536