HP XP7 Storage - Manual (Page 33)

The remaining SM = The whole SM capacity - The SM area used by FS pools
and FS pairs
Related topics
•
“Workflow for calculating Fast Snap pairs based on the snapshot estimated manageable
capacity” (page 32)
.
Workflow for calculating Fast Snap pairs based on cache management devices
Cache management devices are the unit for controlling the cache in association with logical volumes
(LDEVs). They are required to perform FS tasks, such as creating FS pairs for a volume.
Use the following workflow to calculate the number of FS pairs that you can create based on the
number cache management devices:
1. View the number of cache management devices (see “Viewing the number of cache
management devices” (page 110) ).
2. Use the following formula to calculate the number of FS pairs that you can create based on
the number cache management devices:
The number of FS pairs that you can create = the number of cache
management devices / ceil (the P-VOL capacity of FS pairs [TB]) /
2.6 [TB])
Related topics
•
“Calculating the number of cache management devices” (page 33)
•
“Calculating the number of the remaining cache management devices” (page 141) .
Calculating the number of cache management devices
Use the following formula to calculate the number of cache management devices you must reserve
to initially create an FS pair for a volume:
The number of FS pairs that you must reserve = ceil(Size of P-VOL ÷
2.6) (in terabytes)
If the amount of pool usage for the P-VOL exceeds 70 percent of the total capacity of the cache
management devices reserved for the P-VOL, you must reserve another cache management device.
You can reserve a maximum of 256 cache management devices for each P-VOL.
Related topics
•
“Fast Snap cache management device requirements” (page 33) .
Fast Snap cache management device requirements
The following table shows the FS cache management device requirements for performing FS tasks.
Number of cache management device required Task
8,192* Initially create an FS pool.
1 Create a volume.
256 Create a P-VOL
4,097 Initially create an FS pair for a volume.
FS assigns 4,096 of the 8,192 devices that are available.
You can manage up to 65,280 cache management devices in a storage system.
Requirements for Fast Snap tasks 33