Maximum Supported Capacity - Hitachi AMS2100 User Manual

Maximum supported capacity

NOTE: In a dual-controller array, the calculations must be performed for
both controllers.
Hitachi AMS 2000 Family Copy-on-Write SnapShot User Guide
Read/write and pair operations are limited when a SnapShot pair is
cascaded with TCE. Please see the appendix on cascading in the
Hitachi Adaptable Modular Storage TrueCopy Extended Distance
User Guide (MK-DF978054) for full information.
The SnapShot function restricts P-VOL/data pool capacity.
• When SnapShot and ShadowImage are used on the same array
• When ShadowImage is used in addition to SnapShot
The capacity you can assign to SnapShot replication volumes per
controller is limited, for the following reasons:
• The maximum capacity supported by a SnapShot pair depends
on the ratio of P-VOL to data pool and cache memory.
• When using other copy systems and SnapShot together, the
maximum supported capacity of the P-VOL may be restricted
further.
In addition to this, capacity is managed by the AMS array in blocks
of 15.75 KB for data volumes and 3.2 KB for data pools. For example,
when a P-VOL block's actual size is 16 KB, the array manages it as
two blocks of 15.75 KB, or 31.5 KB. Data pool capacity is managed
in the same way but at 3.2 KB per block.
•
This section provides formulas for calculating your existing or
planned SnapShot volume capacity and comparing it to the
maximum supported capacity for your particular controller and its
cache memory size.
SnapShot capacity must be calculated for both of the following:
1. The ratio of SnapShot and TCE (if used) capacity to data pool
capacity. Capacity is calculated using the following volumes:
- SnapShot P-VOLs
- TCE P-VOLs and S-VOLs (if used)
- All data pools
2. Concurrent use of TCE and ShadowImage. If SnapShot is used
concurrently also, it is included in this calculation. Capacity is
calculated using the following volumes, if used:
- SnapShot P-VOLs
- TCE P-VOLs and S-VOLs
- TrueCopy P-VOLs and S-VOLs
- ShadowImage S-VOLs
Planning and design
2-31