Understanding Raid Level-1 Enhanced - IBM Netfinity ServeRAID-3H Installation And User Manual

Understanding RAID Level-1 Enhanced

If you have three or more physical drives in the array, you can no longer select RAID level-1, but you can
select RAID level-1 Enhanced (also called RAID level-1E).
RAID level-1E combines mirroring with data striping. This RAID level stripes data and copies of the data
across all of the drives in the array. As with the standard RAID level-1, the data is mirrored, and the
capacity of the logical drive is 50% of the array capacity of the grouping of physical drives in the array.
RAID level-1E requires a minimum of three drives and, depending upon the level of firmware and the
stripe-unit size, supports a maximum of eight or 16 drives.
The following illustration is an example of an Enhanced RAID level-1 logical drive.
You start with three physical drives.
Create an array using the physical drives.
Then, create a logical drive within that array.
The data is striped across the drives, creating blocks.
Notice that the stripe labeled
* *
stripe labeled is the mirror (that is, the copy) of the
preceding data stripe. Also notice that each block on the
mirror stripe is shifted one drive.
With RAID level-1E, if one of the physical drives fails, the ServeRAID controller switches read and write
requests to the remaining functional drives in the RAID level-1E array.
*
is the data stripe and the
1 2
*
* 3 1
*
x
4 5
*
* *
6 4
3
2
6
5
7
Chapter 1. Getting started