HP XP7 Storage - Manual (Page 78)

Figure 10 Workflow of a new page assignment
Tier relocation workflow: Tier relocation is performed taking advantage of the buffer space allocated
for tier relocation, as mentioned above. Tier relocation is also performed to secure the space
reserved in each tier for new page assignment. The area is called the buffer space for new page
assignments. When tier relocation is performed, Smart Tiers reserves buffer spaces for relocation
and new page assignment.
During relocation, a tier may temporarily be assigned over 98% of capacity as well, or well under
the allowance for the buffer areas.
Further influence on tier relocation and tier occupancy: The buffer area for tier relocation and new
page assignment will influence the amount that a tier’s capacity is used.
If the relocation cycle’s duration is not long enough for the allocation moves to all complete, then
the amount of tier capacity used may not fully represent the desired target levels. Subsequent
relocations should eventually reach the target levels.
Smart Tiers Z cache specifications and requirements
The following cache capacity is required when the total capacity is 128 TB:
•
Recommended capacity of cache memory for data: 28 GB
•
Required capacity of cache memory for control information for using Thin Provisioning Z: 8
GB
•
Required capacity of cache memory for Smart Tiers Z: 4 GB
•
Therefore, in this example 40 GB of capacity of cache memory is required.
Note that cache memory is installed in pairs. Therefore, actual capacity is twice the cache memory
capacity. For example, if required controlling information is 8 GB, then actual installed capacity
is 16 GB.
To decrease the capacity of the cache memory for Smart Tiers Z, you have to remove Smart Tiers
Z.
Execution modes for tier relocation
Execution modes when using Remote Web Console
Smart Tiers Z performs tier relocations using one of two execution modes: Auto and Manual. You
can switch between modes by using Remote Web Console.
78 Configuring thin provisioning