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Re: hard- or software-raid?

Tinus Nijmeijers wrote:

I'm building a server that needs about 200G of harddisk space and the
data has to be safe. If I need to replace a faulty hd and get downtime
that's fine. Speed is not an issue.

The system will boot of a scsi HD, I have a backup boot disk available.

Disks (couple of 120G IDE or something) will be in 1+0, raid5 or raid6
(does software raid do raid6?)

Is there any reason to use hardware-raid over software-raid in this



OK, For booting, I suggest getting a uw or better ie (u2w) scsi hardware raid controller (AMI megatrends seem linux friendly) and 2 x 4gig ultra wide (uw) or bigger disks (raid1 ~ mirrored), you dont need bigger, but bigger disks will be younger and hopefully last longer. An improvement would be 3 x 4 gig disks and have one as a hot spare to the first 2. I wouldnt go older/smaller than 4 gig as 2 gig disks are getting very old and are slower. This will be a robust boot system, software raid is not any good for booting.

Ive never heard of raid 6 (commercially anyway).

Since speed is not your issue I suggest Raid 5 using software raid for the data. Ive found it no worse performance wise than hardware raid (on ide anyway) and way cheaper. Ive pulled a disk out of a software raid 5 setup and re-inserted it and the system recovered fine (that was scsi mind). These days CPU's are not usually the bottleneck in server performamce so the penalty of the raid 5 calculations on the CPU seems insignificant.

Raid 5 needs at least 3 disks, as one disk is lost on parity, so your options for 200 gig are 3 x 100 or 120 gig drives giving you 200 ~ 240gig of usuable space or 4 x 80 gig disks also giving you 240gig of raid 5.

3 disks is good as then if you so choose you can add an extra disk as a hot spare, this way if one dies you rebuild on line and swap the dead one out at your convienience. That means paying for an extra disk mind....

If you want to improve performance only put 1 ide disk per channel, this means an extra ide controller (ie 2, assuming 2 channels per controller), but there should be a speed improvement.



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