Note: In a multiple tier pool volume, metadata is allocated on the upper tiers to
provide maximum performance. Unless Nearline drives are the only tier in the
pool, the metadata is never allocated on this tier. If Flash/SSD is in the pool, then
metadata is allocated first on this tier and then on Enterprise drives (if available).
A pool with 10% Flash/SSD or greater would have all of the volume metadata on
this tier.
A simple way of estimating the maximum space that might be used by volume
metadata is to use the following calculations:
FB Pool Overhead = (#volumes*2 + total volume extents / 10)/64 - rounded up
to the nearest integer
CKD Pool Overhead = (#volumes*2 + total volume extents / 10)/53 - rounded up
to the nearest integer
These calculations overestimate the space that is used by metadata by a small
amount, but the precise details of each volume do not need to be known.
Examples:
v For an FB storage pool with 6,190 extents in which you expect to use thin
provisioning and allocate up to 12,380 extents (2:1 overprovisioning) on 100
volumes, you would have a pool overhead of 23 extents -> (100*2+12380/10)/
64=22.46.
v For a CKD storage pool with 6,190 extents in which you expect to allocate all the
space on 700 volumes, then you would have a pool overhead of 39 extents ->
(700*2+6190/10)/53=38.09.
RAID capacities for DS8880
Use the following information to calculate the physical and effective capacity for
DS8880.
RAID capacities for High Performance Flash Enclosures Gen2
RAID 6 is the recommended and default RAID type for all drives over 1 TB. RAID
6 and RAID 10 are the only supported RAID types for 3.8 TB Flash Tier 1 drives.
RAID 6 is the only supported RAID type for 7.6 TB Flash Tier 2 drives.
Table 39. RAID capacities for High Performance Flash Enclosures Gen2
Flash Tier 0,
Flash Tier 1, or
Flash Tier 2
drives disk size
Physical
capacity of
Flash Tier
0, Flash
Tier 1, or
Flash Tier
2 drives set Rank type
Effective capacity of one rank in number of extents
RAID-10 arrays RAID-5 arrays RAID-6 arrays
3 + 3 4 + 4 6 + P 7 + P 5 + P + Q 6 + P + Q
400 GB 6.4 TB FB Lg Ext 1049 1410 2132 2493 1771 2132
FB Sm Ext 67170 90285 136507 159607 113393 136495
CKD Lg Ext 1177 1582 2392 2797 1987 2392
CKD Sm Ext 62388 83858 126797 148256 105328 126787
800 GB 12.8 TB FB Lg Ext 2133 2855 4300 5023 3578 4300
FB Sm Ext 136542 182781 275254 321475 229015 275239
CKD Lg Ext 2392 3203 4823 5633 4013 4823
CKD Sm Ext 126821 169768 255651 298601 212705 255655
1.6 TB 25.6 TB FB Lg Ext 4301 5746 n/a n/a 7191 8636
FB Sm Ext 275284 367771 n/a n/a 460243 552727
CKD Lg Ext 4824 6445 n/a n/a 8065 9686
CKD Sm Ext 255684 341586 n/a n/a 427475 513372
94 DS8880 Introduction and Planning Guide
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