Mirrored Raid Performance; Other Performance Options - Intergraph InterRAID-12 Hardware User's Manual

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Performance will benefit because the separate channels work independently of each other.
Multiple I/O requests can occur simultaneously since they are on separate channels of the
controller.
An extension of this technique is to stripe not only across multiple SCSI channels on a single
controller but to stripe across multiple controllers. You can accomplish this by combining
drives on individual controllers in the manner described above. Then, create one (or more)
logical drive on each RAID controller and use the disk striping capabilities built into
Windows NT Server to stripe these logical drives together into a logical volume.

Mirrored RAID Performance

When mirroring data (such as RAID 1), the packs should not span the channels. You should
create two packs, each on its own channel. For example, perform the following using four
1 GB disk drives:
u
Put the first disk drive into the first pack on the first I/O channel of the RAID controller.
u
Put the second disk drive into the first pack on the first I/O channel of the RAID
controller.
u
Put the third disk drive into the second pack on the second I/O channel of the RAID
controller.
u
Put the fourth disk drive into the second pack on the second I/O channel of the RAID
controller.
Notice that mirroring increases the size to 2 GB. By creating two packs on separate
channels and mirroring the first pack to the second pack, the mirrored data writes
simultaneously as the original data. Simultaneous writing results in improved performance.
However, if you do not keep the packs on separate channels, performance will degrade
because one channel will possibly have to sequentially write the original data and the
mirrored data.

Other Performance Options

Other I/O options that can help performance are Tagged Command Queuing, Write Back
Caching, and Controller Read Ahead. Careful distribution of data can also increase
performance.