On 2/14/2012 10:59 AM, Jerry Feldman wrote:
One issue with RAID is that you don't want to mix geometries. I like to keep 2 different makes of drives in my RAID because of different MTBFs. We've had simultaneous drive failure in the BLU servers, With 2 different makes (or at least 2 different lot numbers) the chances of simultaneous disk failure is lower.
Small differences in geometry (slightly different numbers of blocks) aren't a problem; you just create the partitions to match the smallest drive. If the leftover space is large enough you can use it for a variety of purposes, including a boot partition (even a RAID 1 pair of them if you have a couple of matching spaces) or swap. Setting up boot from a RAID 5 is a pain if your distro supports it at all, so a vanilla boot partition is handy. Small amounts of leftover space get wasted, but what's a stray GB among friends?
Large differences and/or differences in block size are best avoided, though after the first 200GB drive failure it was replaced with a 250GB drive because 200GB drives were no longer readily available.
I ran a RAID 5 server with five 200GB drives for a few years; it was a media server for storing my music and video collection. There were three different brands of drives, and no two drives were from the same manufacturing lot as I had bought them one at a time whenever special deals were offered. I suffered two drive failures over that period, but they were widely separated and no data was ever lost.
After the second failure I replaced that with a RAID 1 pair of 1.5TB drives, and reused the four good drives in other servers (two servers with RAID 1 pairs in two email servers, one at my house and one at a friend's house). All are currently going strong.
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