Chris Hedemark on Thu, 27 Feb 2003 07:03:07 -0500


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Re: [PLUG] organizing files on software Raid (SCSI)


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On Thursday, February 27, 2003, at 09:26 AM, Wayne Dawson wrote:

No, actually this is the first time I've used RAID. My boss is much more familiar with RAID, and he decided what raid levels we should use for which machines. What can you tell me about it?

The common RAID levels you are likely to run into, high level overview:

0 - No raid at all, really. This is just striping a bunch of disks together with zero redundancy. Fast R/W performance, zero loss of capacity.
1 - Mirroring. Fast R/W performance, 50% loss of capacity.
5 - Striping with parity. Fast read performance, lousy write performance, as much as 33% loss of capacity.
10 & 0+1 - Combination of striping & mirroring (you can have mirrored stripe sets or striped mirror sets). R/W performance is excellent, 50% loss of capacity.


RAID 5 definitely gives you the most usable capacity, but too many dive into it without realizing that disk writes are going to be slower than SLED (single large expensive disk). The performance hit will be somewhat reduced since you are talking about hardware RAID 5 (software RAID 5 is a dog). If I were running a public ftp mirror, or serving up lots of static HTML, RAID 5 would make more sense since the read operations are fast and I get to use more of my disk.

But if write performance is important, I'm going to pick hardware RAID 10 (or 0+1, whichever of the two your hardware allows) every time.

Chris Hedemark
PGP/GnuPG Public Key at http://yonderway.com/chris/hedemark.gpg
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