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RAID or no RAID?

By Hakor Erawan ·
I am purchasing two IBM rack servers for a group. One will sit onsite and the other offsite as a backup. Onsite replicates to offsite using Legato Replistor over a WAN link. However, in addition to the failover, I also want to have local redundancy and fault tolerance. The IBM server is an xSeries 345 2.8Ghz which offers 6 hotswap drives with integrated RAID 1. I know the server will be heavily written to and read from as there will be a database of documents stored on it that is expected to grow up to 200GB or more. I'm stuck as how to implement RAID on such a system. Should I mirror the OS on two drives and RAID 5 the last 4 slots? What space considerations are needed? What performance hits will occur if I used Windows 2000 Server RAID as opposed to hardware RAID?

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Software Raid: JUST SAY NO!

by TomSal In reply to RAID or no RAID?

Or I could have said "Friends don't let friends use software raid".

Definitely pursue a hardware raid option, with as much mem on the raid controller as you can possibly afford.

You also have the right idea with mirroring the OS, IMHO in any production server with multiple drives and the need for fault tolerance (which is actually ALL production servers) mirrored OS drives is required and should be implemented without hesitation.

As far as space constraints, remember to calculate your space with Raid 5 - do NOT include one full drive in your estimations, because one drive is "lost" to parity.

So if you are aiming for 200 gbs of space and say you have (just an example) four 50 gig drives you won't meet your 200 gigs of space. First you'll lost 50 to parity and then there's the normal overhead of formating and the filesystem that just can't be avoided.

You aren't that far off track though! Mirror the OS, and yes RAID 5 isn't a bad choice for fault tolerance. We have Raid 5 on our master DB and that gets pounded all day long every day.

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by Hakor Erawan In reply to Software Raid: JUST SAY N ...

Yes very true, but I have used Windows 2000 RAID on some servers, just for simple mirroring on dynamic disks.

But this is different. This server will run MS SQL 2000 and the data will sit locally across the RAID 5 config. The RAID card is incredibly expensive (256MB cache and over 1 grand). I expect the OS and MS SQL to reside on two 36GB disks in RAID 1. For the rest, 4 x 73GB drives which is really 3 x 73GB for the data in RAID 5.
Theoretically it looks ok, but as I've said, there will be constant r/w activity so it all depends on the hardware as well.

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