The same capacity drives and the same kind of drives (SSDs or SED SSDs) must be used to configure a RAID
group.
Figure 8 Example of a RAID Group
RAID group 1 RAID group 2
SSD
400GB
S
SD
960GB
SSD
960GB
SSD
960GB
SSD
960GB
SSD
400GB
SSD
400GB
SSD
400GB
SSD
400GB
Use drives that have the same capacity to configure RAID groups.
If a RAID group is configured with drives that have different capacities, all the drives in the RAID group are
recognized as having the same capacity as the drive with the smallest capacity in the RAID group and the rest
of the capacity in the drives that have a larger capacity cannot be used.
Table 6 shows the recommended number of drives that configure a RAID group.
Table 6 Recommended Number of Drives per RAID Group
RAID level
Number of configura-
tion drives
Recommended number of drives (*1)
RAID1+0 4 to 32 6(3D+3M), 8(4D+4M), 10(5D+5M)
RAID5 3 to 16 4(3D+1P), 5(4D+1P), 6(5D+1P), 7(6D+1P), 8(7D+1P)
RAID5+0 6 to 32
4(3D+1P) ´ 2, 5(4D+1P) ´ 2, 6(5D+1P) ´ 2
RAID6 5 to 16 5(3D+2P), 6(4D+2P), 7(5D+2P), 8(6D+2P)
RAID6-FR 11 to 31
17 ((6D+2P) ´2+1HS)
*1: D = Data, M = Mirror, P = Parity, HS = Hot Spare
•
Sequential access performance hardly varies with the number of drives for the RAID group.
•
Random access performance tends to be proportional to the number of drives for the RAID group.
•
Use of higher capacity drives will increase the time required for the drive rebuild process to complete.
•
For RAID5, RAID5+0, and RAID6, ensure that a single RAID group is not being configured with too many
drives.
If the number of drives increases, the time to perform data restoration from parities and Rebuild/Copyback
when a drive fails also increases.
For details on the recommended number of drives, refer to Table 6.
•
The RAID level that can be registered in REC Disk Buffers is RAID1+0. The drive configurations that can be
registered in REC Disk Buffers is 2D+2M or 4D+4M.
For details on the Thin Provisioning function and the RAID configurations that can be registered in Thin Pro-
visioning Pools, refer to "Storage Capacity Virtualization" (page 46
).
An assigned CM is allocated to each RAID group. For details, refer to "Assigned CMs" (page 102).
1. Function
RAID Functions
24
FUJITSU Storage ETERNUS AF250 S2, ETERNUS AF250 All-Flash Arrays
Design Guide (Basic)
Copyright 2019 FUJITSU LIMITED
P3AG-1822-09ENZ0
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