HP XP P9500 Storage - Manual (Page 88)

tier. The buffer space for tier relocation is 2% in all tiers. The following illustrates the workflow of
new page assignment.
Figure 5 Workflow of a new page assignment
NOTE: If you specify the new page assignment tier to THP V-VOL, the tier to which a new page
is assigned can be specified. In the default setting, a new page is assigned from the middle tier
and you can specify the tier to which the new page is assigned. The default setting is a new page
assigned from the middle tier.
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.
Buffer space: The following table shows the default rates (rate to capacity of a tier) of buffer space
used for tier relocation and new page assignments, listed by drive type. The default values can be
changed, if needed, using Storage Navigator or RAID Manager.
Total buffer area for new page
assignment buffer area for tier relocation Drive type
2% 0% 2% SSD
10% 8% 2% Non-SSD
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 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: 8 GB
88 Configuring thin provisioning