[ILUG] Dell PERCs and Linux

[Paul Jakma]

On Sat, 17 Jun 2000, David Murphy wrote:

> If you only ever run one process at a time, definitely, otherwise, we
> don't yet know who they compare.

????

what does single/multiple processes have to do with it? the raid
card/software has no concept of processes.

if you mean low/high I/O pressure: again that's irrelevant! at this
this low level the only metric is bit rate - and RAID0 is king,
followed by RAID5 (for reads). RAID1 is last.

if you mean the pattern of I/O (random vs seq'tial), bit-rate is
still king. Even though RAID1 per block seek time is lower ( =<
highest seek time of component disks + disk read) than RAID5. (=
highest seek time + 3 disk read[1]), over a collection of random disk
blocks RAID5 should still win because of it's greater bit-rate.

that is what i have seen. You argue there must be a deficiency
therefore in linux RAID1[2]. However i (and others) still feel that
RAID5 as a technology /must/ be faster than RAID1. 

Either accept the weight of opinion and let the thread die, or come
up with numbers.

regards,
-- 
Paul Jakma	paul at clubi.ie
PGP5 key: http://www.clubi.ie/jakma/publickey.txt
-------------------------------------------
Fortune:
In defeat, unbeatable; in victory, unbearable.
		-- W. Churchill, on General Montgomery

[1]. Although this could be done in parallel with multiple
controllers. 

[2]. you cited round-robin reads a la Sun. However linux does do
this.