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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Summary of Contents for DS8880 Series
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