[Techtalk] Made RAID Mistake?

[Malcolm Tredinnick]

On Sun, Jan 12, 2003 at 10:32:43PM -0500, Andrew wrote:
> 	The nugget posted by Kelly is great for giving prospective to
> 	nubies like myself.  Thank you.  I read a theory piece that
> 	questioned the need for hardware Raid now that 100,133 and SCSI
> 	160MHz are available on the board or with less expensive
> 	non-raid cards. Using intelligent partitioning, LVM and maybe
> 	software raid should give satisfactory results.  I am interested
> 	in opinions of the experienced people here. Maybe I am missing
> 	part of the concept?

We use RAID here at work on a number of largish arrays (nearly half a
terrabyte on a few machines and we are collecting the bits for a
terrabyte+ machine for testing). In all cases we have gone with software
RAID with IDE drives under Linux, simply for the convenience and cost.
As Kelly mentioned, the "trick" with hardware RAID is getting the
drivers for the card to cooperate transparently with the OS. After
briefly wrestling with that option, we just switched to using Promise
controller cards (to provide multiple IDE ports) and software RAID. So
far (a year of fairly heavy use) no problems.

The decisive factors here were that IDE is still significantly cheaper
per megabyte than SCSI (even when we factored in mean times to failure,
since we expect to have to replace IDE drives more often than we might
replace the more expensive SCSI counterparts). Also, all of our big
datasets are stored in duplicate on multiple machines, so we can handle
individual drives failing (through RAID) and entire machines or
controller cards failing (through data synchronisation with second and
third machines).

If we had extremely high speed read and write requirements, SCSI might
have been important. Similarly, if handling the failure of individual
drives was difficult, then the more reliable SCSI drives would come into
consideration (although -- recent Fujitsu disasters aside -- IDE drives
are pretty reliable these days).

Malcolm

-- 
Borrow from a pessimist - they don't expect it back.