[rescue] Re: RAID

[Greg A. Woods]

[ On Tuesday, July 10, 2001 at 12:56:02 (-0700), Robert Novak wrote: ]
> Subject: [rescue] Re: RAID (was Re: Insane drives)
>
> RAID5 with good sparing can be pretty good. Note that some of these
> comments on RAID5 also apply to RAID3 or RAID4, since the base concepts
> are somewhat similar.
> 
> In general though, * sucks. Or .* for you regexp fans.

> RAID-5 with a hardware controller and hefty battery-backed cache can be
> quite usable. I actually had 3 18gb disks on a Mylex controller with 8MB
> of cache, RAID-5, and it was comfortable. Darned slow to build the set,
> but once it was there, FreeBSD ran happily on it.

RAID-5, with enough cache, and with proper tuning of the stripe size to
match both the cache handling algorithms and the OS read/write block
sizes, can really fly; at least so long as you're not trying to get 100%
of your disk bandwidth 100% of the time (which in my experience usually
only happens during benchmarks!  ;-).

Obviously if you don't have a lot of excess CPU power then having a
separate processor for managing the RAID set, parity calculations, etc.,
is absolutely necessary.  With many operating systems the issue of
having separate cache also dictates doing a "hardware" RAID
implementation.....

These CMD CRD-5500 controllers I've got are real wonders!  I just wish I
could find enough spare large SIMMs to stuff them up to 512MB RAM each!  ;-)

-- 
							Greg A. Woods

+1 416 218-0098      VE3TCP      <gwoods at acm.org>     <woods at robohack.ca>
Planix, Inc. <woods at planix.com>;   Secrets of the Weird <woods at weird.com>