Hitachi AMS2100 User Manual page 90

NOTE: When SnapShot is enabled, a portion of cache memory is assigned
to it. Please review
more information.
2-38
Hitachi AMS 2000 Family Copy-on-Write SnapShot User Guide
Example
In the following example, array and cache memory capacity are
AMS2100 and 2 GB.
SnapShot: Maximum supported capacity value of P-VOL (TB)
= Maximum SnapShot single capacity
- (Total ShadowImage S-VOL capacity / 17)
- (Total TrueCopy P-VOL and S-VOL capacity / 17)
- (Total TCE P-VOL and S-VOL capacity x 3
1. SnapShot Maximum single capacity = 46 TB
2. Divide the total ShadowImage S-VOL capacity by 17. For
example:
Total SI S-VOL = 4 TB (4000 GB)
4000 GB / 17 = 235.3 GB
3. Subtract the quotient from the TCE maximum single capacity. For
example:
46 TB (46000 GB) - 235 GB = 45765 GB
4. Divide the total TrueCopy P-VOL and S-VOL capacity by 17. For
example:
Total TrueCopy P-VOL and S-VOL capacity = 20 TB (20000
GB)
20000 GB / 17 = 1176 GB
5. Subtract this quotient from the remaining SnapShot maximum
single capacity. For example:
45765 GB - 1176 GB = 44589 GB
6. Multiply total TCE P-VOL and S-VOL capacity by 3. For example:
Total TCE P-VOL and S-VOL capacity = 600 GB
600 GB x 3 = 1800 GB
7. Subtract this product from the remaining SnapShot maximum
single capacity. For example:
44589 GB - 1800 GB = 42789 GB, the capacity left for
SnapShot P-VOLs on the controller.
•
Appendix D, SnapShot with Cache Partition Manager
If your system's maximum capacity exceeds the maximum allowed
capacity, you can do one or more of the following:
• Change the P-VOL size
• Reduce the number of P-VOLs
• Change the data pool size
• Reduce the number of V-VOLs
• Reduce the lifespan of the V-VOL
Planning and design
for