IBM ServeRAID, User Reference

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RAID level-5 offers the following advantages and disadvantages.
Advantages Disadvantages
v 100% data protection
v Offers more physical drive storage
capacity than RAID level-1 or level-1E
Lower performance than RAID level-1 and
level-1E
Understanding RAID level-5 Enhanced
RAID level-5E is the same as RAID level-5 with a built-in spare drive. Like RAID
level-5, this RAID level stripes data and parity across all of the drives in the array.
RAID level-5E offers both data protection and increased throughput. When an array
is assigned RAID level-5E, the capacity of the logical drive is reduced by the
capacity of two physical drives in the array (one for parity and one for the spare).
Reading from and writing to four physical drives is more efficient than reading from
and writing to three physical drives and an idle hot spare. Therefore, RAID level-5E
provides a higher level of performance than RAID level-5.
The spare drive is actually part of the RAID level-5E array, as shown in the
following example. With such a configuration, you cannot share the spare drive with
other arrays. If you want a spare drive for any other array, you must have another
spare drive for those arrays.
RAID level-5E requires a minimum of four drives and, depending upon the level of
firmware and the stripe-unit size, supports a maximum of 8 or 16 drives. RAID
level-5E is also firmware-specific.
Note: For RAID level-5E, you can have only one logical drive in an array. When
using RAID level-5E, you can have a maximum of seven logical drives on
the controller.
The following illustration is an example of a RAID level-5E logical drive.
Start with four physical drives.
Create an array using all four physical
drives.
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IBM ServeRAID: User’s Reference, Version 5.10