The Shoes of the Fisherman's Wife Are Some Jive-Ass Slippers

Sun, 31 Oct 2004

Interesting RAID setup

On the latest Ask Slashdot there is an article about Experiences w/ Software RAID 5 Under linux. (It's better than the usual Ask Slashdot posting whose answer can be found by using Google).

A poster comments:

FWIW, here's the system I've evolved for partitioning disks in such systems:

• First partition: One cylinder (the innermost one): Ext FS containing a THIS_DISK file in which I record when and why I bought the drive and any interesting history it has had. In an emergency when you're suddenly shuffling eight hot drives plus a couple spares plus a dead and replacement motherboard &tc, you WILL lose track of which disk was doing what. This little partition will save you a lot of grief.

• Second partition: Swap, in the outermost (lowest numbered) cylinders -- because these give the fastest transfer rates, up to about a 50% advantage. Putting swap on every disk lets the kernel stripe swaps across all available drives for additional parallellism and speed, and also ensures you've got adequate swap no matter how you configure in an emergency.

• Third partition: RAID2, a complete bootable Linux system. With this mirrored on every drive in the system, you're guaranteed able to get up again fast no matter what goes wrong. Thus, FD partition type.

• Fourth partition: RAID5, your serious filestore space, occupying the vast majority of the disk.

(He/she also mentions that the fourth partition can be RAID2 for workstation machines).

A system like this would make a nice NAS setup for a small business or small office server. The nicest property here is that every disk can contain the NAS software and thus have minimal downtime if the system disk dies.

This setup probably doesn't scale too well above a small handful of disks, kind of like the number of superblocks written by Linux 2.0 ext2fs. Having a complete copy of the system partition on every single disk may be overkill.