IBM DS8880 Series Introduction And Planning Manual page 106

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Table 39. RAID capacities for High Performance Flash Enclosures Gen2
Physical
capacity of
Flash Tier
Flash Tier 0, 0, Flash
Flash Tier 1, or Tier 1, or
Flash Tier 2 Flash Tier
drives disk size 2 drives set Rank type
400 GB 6.4 TB
800 GB 12.8 TB
1.6 TB 25.6 TB
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DS8880 Introduction and Planning Guide
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.
RAID-10 arrays
3 + 3
FB Lg Ext 1049
FB Sm Ext 67170
CKD Lg Ext 1177
CKD Sm Ext 62388
FB Lg Ext 2133
FB Sm Ext 136542
CKD Lg Ext 2392
CKD Sm Ext 126821
FB Lg Ext 4301
FB Sm Ext 275284
CKD Lg Ext 4824
CKD Sm Ext 255684
Effective capacity of one rank in number of extents
RAID-5 arrays
4 + 4 6 + P 7 + P
1410 2132 2493
90285 136507 159607
1582 2392 2797
83858 126797 148256
2855 4300 5023
182781 275254 321475
3203 4823 5633
169768 255651 298601
5746 n/a n/a
367771 n/a n/a
6445 n/a n/a
341586 n/a n/a
RAID-6 arrays
5 + P + Q 6 + P + Q
1771 2132
113393 136495
1987 2392
105328 126787
3578 4300
229015 275239
4013 4823
212705 255655
7191 8636
460243 552727
8065 9686
427475 513372