[RndTbl] RAID5 rebuild performance

Kevin McGregor kevin.a.mcgregor at gmail.com
Fri May 20 18:23:41 CDT 2011

Yeah, I've read something about limiting the SCSI chain to 4 drives. Alas,
not possible in my situation. 272 MB/s read from a RAID10 is possibly the
practical upper limit, despite the drives being easily able to exceed that.
When I'm back at work on Tuesday I'll do a couple of quick tests of the
RAID5 array.

On Fri, May 20, 2011 at 5:08 PM, Adam Thompson <athompso at athompso.net>wrote:

> In any event, yes, a single U320 bus can only do 320MB in aggregate, and
> its practical limit is around 80% of that.  HP's external enclosures are not
> exactly notorious for being well-balanced equipment...
> Only one model in any given product generation will be a single-bus design,
> that's the economy model.
> On a Sun E450 with Ultra-II (40MB/sec) drives, the system backplane is
> engineered so that no more than 4 drives are connected to any one channel,
> for example.
> Generally speaking, the 4-disk per channel limit is sound engineering.
> There's also a curious effect that I've seen but can't explain where more
> spindles actually slows down the array drastically... I suspect if you
> recreate that array as RAID 50, you'd see performance gains.
> -Adam
> Trevor Cordes <trevor at tecnopolis.ca> wrote:
> >On 2011-05-20 Kevin McGregor wrote:
> >> When the SCSI controller BIOS is initialized, it lists all of the
> >> drives on both channels, and most of them (as I recall) are described
> >> as being set to 80 MB/s with a note that the OS will probably set
> >
> >Weird, see if the SCSI BIOS setup screens let you manually select the
> >SCSI speed.  You might have to drill down to the per-drive area.  I
> >know my U320 card gives me choices.
> >
> >80MB/s per drive isn't shabby, though your drives can probably push
> >100-150MB/s.
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