[ILUG] Why RAID

[John P. Looney]

On Tue, Jul 20, 2004 at 10:23:41PM +0100, Des Keane mentioned:
> At risk of labouring the point, but another nice thing about RAID 1+0 is
> the resync time. Say 4+4 73GB disks, or 4(1+1) since you're into maths
> today! With RAID 1+0 you get to resync 73GB of data if you lose a single
> disk and replace it (hot spare or otherwise). With RAID 0+1 in the same
> scenario you get to twiddle your thumbs whilst performance dives in
> resyncing 292GB of data.

 We did some tests yesterday. DL380 with 2GB RAM, a pair of 2.8Ghz CPUs,
and six 36GB 15k RPM drives. HPs do RAID1+0 and RAID5 in hardware, at
speed - both at just over 40MB/sec for writes.

 We did a pair of parallel kernel compiles. RAID1+0 came in a smidgin
faster, at 47 minutes 41 seconds, while RAID5 did the same job in 47
minutes 46 seconds.

 I've a feeling that the limitation we are seeing is the hardware RAID
card itself though. If I get bored some day, and find I have more really
fast disks, I'll try the same with software RAID.

john