Re: Software RAID5 with 2.6.0-test

[Bill Davidsen <davidsen@tmr.com>]

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On Thu, 9 Oct 2003, Andre Tomt wrote:

> On Thu, 2003-10-09 at 10:55, Måns Rullgård wrote:
> > > Was this a 4 port or 2 port HPT controller? Keep in mind, two disks on
> > > the same IDE channel severely degrades performance, *especially* with
> > > RAID.
> > 
> > It's a four port SATA controller.  I'd never even think about placing
> > two disks on the same cable.
> 
> You can't either, considering it is SATA :-)
> 
> However, I wouln't count on superior performance from software based
> RAID 5 (ata/fakeraid or otherwise), that is whats real raid controllers
> are for.

While an overloaded system may benefit from offloaded the CPU
requirements of RAID, unless you go to a very expensive external unit
the kernel RAID will usually outperform the inexpensive RAID embedded on
a controller. The kernel simply knows more about the data needs and can
can do things a controller can't.

You can also use only part of a drive, by partition, in a RAID group,
leaving the rest to be used as dumb disk. Very cost effective, if only a
part of the data justified mirroring, you don't need to mirror whole
drives. Yes, that's a cost vs. speed tradeoff, but an effective one
where reliabiity is needed, but performance is not critical.

-- 
bill davidsen <davidsen@tmr.com>
  CTO, TMR Associates, Inc
Doing interesting things with little computers since 1979.