User Capacity (Logical Capacity); Table 4 Formula For Calculating User Capacity For Each Raid Level - Fujitsu ETERNUS DX100 S4 Design Manual

2. Basic Functions
RAID Functions
*1: Performance may differ according to the number of drives and the processing method from
the host.
■
Recommended RAID Level
Select the appropriate RAID level according to the usage.
Recommended RAID levels are RAID1, RAID1+0, RAID5, RAID5+0, RAID6, and RAID6-FR.
•
When importance is placed upon read and write performance, a RAID1+0 configuration is recom-
•
mended.
For read only file servers and backup servers, RAID5, RAID5+0, RAID6, or RAID6-FR can also be
•
used for higher efficiency. However, if the drive fails, note that data restoration from parities and
rebuilding process may result in a loss in performance.
For SSDs, a RAID5 configuration or a fault tolerant enhanced RAID6 configuration is recommen-
•
ded because SSDs operate much faster than other types of drive. For large capacity SSDs, using a
RAID6-FR configuration, which provides excellent performance for the rebuild process, is recom-
mended.
Using a RAID6 or RAID6-FR configuration is recommended when Nearline SAS disks that have
•
6TB or more are used. For details on the RAID levels that can be configured with Nearline SAS
disks that have 6TB or more, refer to

User Capacity (Logical Capacity)

User Capacity for Each RAID Level
The user capacity depends on the capacity of drives that configure a RAID group and the RAID lev-
el.
Table 4 shows the formula for calculating the user capacity for each RAID level.

Table 4 Formula for Calculating User Capacity for Each RAID Level

RAID level
RAID0
RAID1
RAID1+0
RAID5
RAID5+0
RAID6
RAID6-FR
*1: "N" is the number of RAID6 configuration sets. For example, if a RAID6 group is configured with
"(3D+2P)´2+1HS", N is "2".
Fujitsu Storage ETERNUS DX100 S4/DX200 S4, ETERNUS DX100 S3/DX200 S3 Hybrid Storage Systems Design Guide (Basic)
"Supported RAID" (page
Formula for user capacity computation
Drive capacity ´ Number of drives
Drive capacity ´ Number of drives ¸ 2
Drive capacity ´ Number of drives ¸ 2
Drive capacity ´ (Number of drives - 1)
Drive capacity ´ (Number of drives - 2)
Drive capacity ´ (Number of drives - 2)
Drive capacity ´ (Number of drives - (2 ´ N) - Number of hot spares)
(*1)
22
Copyright 2023 Fujitsu Limited
16).
P3AM-7642-32ENZ0