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Evaluation of RAID

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by jbwconsulting

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I know the basic concepts of RAID(s) but I'm damned if I can find a clear evaluation. I'm looking for server solutions in a 15-20 user environment with a sluggish database.

The original premise of RAID was better performance using cheap disks. Gradually that evolved, in higher incarnations of RAID, to include fault tolerance (parity), which downgrades performance especially on writes, and especially with IDE (cheap) drives.

In other words, most of the performance is gone and instead you've got fault tolerance/redundancy.

Mirroring seems different from parity. Parity would seem to suggest that limited scope errors can be corrected by storing a limited amount of additional data on the same drives (RAID5); however, full redundancy (mirroring) requires complete duplication of the data on a separate drive.

OK, OK, the questions:

1. Does RAID[>0] really produce net performance gains?
2. Why bother with RAID if you want redundancy? Why not just mirror? At the most it saves 1 drive in 4, but adds complexity.
3. If there is a benefit to RAID (as opposed to mirroring) what is the cost?

Am I way off base here?

5 replies

by diabetic

I am, by no means, an expert on RAID. However, in the finest traditions of echRepublic, allow me to share what I *think* I know.

1. Does RAID[>0] really produce net performance gains?

I have heard the same claims, but have not been able to substantiate them.

2. Why bother with RAID if you want redundancy?
Why not just mirror? At the most it saves 1 drive in 4, but adds complexity.

We both mirror and RAID where I work, and we've found that with the 900+ small servers we have, a two-drive solution where we mirror is perfect.

In the 100+ larger servers, where we have 2 (SYS & DATA) addressable drives, we uses a RAID solution.

3. If there is a benefit to RAID (as opposed to mirroring) what is the cost?

My impression is that RAID is best for creating large drives, or for solutions that require protecting multiple drives, or for solutions were you need lots of redundancy, and cost is not a factor. Mirroring is perfect for the single-drive solution, and it is low cost since it only requires the addition of another drive.

But, as I said at the beginning, I'm far from being an expert on this stuff.

Humbly submitted,
diabetic

by diabetic

I am, by no means, an expert on RAID. However, in the finest traditions of echRepublic, allow me to share what I *think* I know.

1. Does RAID[>0] really produce net performance gains?

I have heard the same claims, but have not been able to substantiate them.

2. Why bother with RAID if you want redundancy?
Why not just mirror? At the most it saves 1 drive in 4, but adds complexity.

We both mirror and RAID where I work, and we've found that with the 900+ small servers we have, a two-drive solution where we mirror is perfect.

In the 100+ larger servers, where we have 2 (SYS & DATA) addressable drives, we uses a RAID solution.

3. If there is a benefit to RAID (as opposed to mirroring) what is the cost?

My impression is that RAID is best for creating large drives, or for solutions that require protecting multiple drives, or for solutions were you need lots of redundancy, and cost is not a factor. Mirroring is perfect for the single-drive solution, and it is low cost since it only requires the addition of another drive.

But, as I said at the beginning, I'm far from being an expert on this stuff.

Humbly submitted,
diabetic

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