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Appendix B: Understanding RAID ● 67
Drive segment size is limited to the size of the smallest disk drive in the array. For instance, an
array with two 250 GB disk drives and two 400 GB disk drives can create two mirrored drive
segments of 250 GB, for a total of 500 GB for the array, as shown in the following figure.
Selecting the Best RAID Level
Use this table to select the RAID levels that are most appropriate for the logical drives on your
storage space, based on the number of available disk drives and your requirements for
performance and reliability.
Disk drive usage, read performance, and write performance depend on the number of drives in
the logical drive. In general, the more drives, the better the performance.
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
250 GB
250 GB
400 GB
400 GB
Disk Drives in Logical Drive
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
RAID 10 Lo
g
ical Drive = 500 GB
1
2
1
2
Not Used
Not Used
3
4
3
4
500
499
500
499
...
...
...
...
Unused Space: 150 GB
Unused Space: 150 GB
Drive Segment Size (Smallest Disk Drive)
RAID
Level Redundancy
Disk Drive
Usage
Read
Performance
Write
Performance
Built-in
Hot Spare
Minimum
Disk
Drives
RAID 0 No 100% www www No 2
RAID 1Yes50%wwwwNo2
RAID
10
Yes 50% ww ww No 4