HP XP Racks - Manual (Page 23)

Required shared memory capacity Total capacity of all pools
32 GB If the total capacity satisfies both of following:
• More than 3.4 PB
•
7.9 PB or less
48 GB If the total capacity satisfies both of following:
•
More than 7.9 PB
•
12.3 PB or less
About cache management devices
Cache management devices are associated with volumes (LDEVs) and used to manage caches.
One volume (LDEV) requires at least one cache management device. An entire system can manage
up to 65,280 cache management devices. A THP V-VOL may require more than one cache
management device. This topic describes how to calculate the number of cache management
devices.
Calculating the number of cache management devices required by a THP V-VOL
The number of cache management devices that a THP V-VOL requires depends on the capacity of
the V-VOL (capacity of the user area) and the maximum capacity of cache management device.
The maximum capacity of cache management device depends on the pool attribute (internal volume
or external volume) associated with V-VOL. The following table explains the relationship between
the pool attribute and the maximum capacity of cache management device.
Maximum capacity of cache management device
Maximum capacity
(in blocks)
Maximum capacity
(in MB)
Pool attribute
6,442,082,304 3,145,548 Internal volume
(2.99 TB)
6,442,082,304 3,145,548 External volume
(2.99 TB)
Use the following formula to calculate the number of cache management devices that a THP V-VOL
requires. In this formula, the user-specified capacity is the user area capacity of a V-VOL.
ceil(user-specified capacity ÷ max-capacity-of-cache-management-device)
The calculated value must be rounded up to the nearest whole number.
Calculating the number of cache management devices required by a volume that is
not a THP V-VOL
One volume that is not a THP V-VOL requires one cache management device.
Viewing the number of cache management devices
Click Actions and select View Management Resource Usage to display the number of cache
management devices in the View Management Resource Usage window. For details, see
“About
cache management devices” (page 23) and “View Management Resource Usage window”
(page 308) .
About cache management devices 23