Chris Mauritz wrote:
>
> > From [EMAIL PROTECTED] Sat Apr 22 21:37:37 2000
> >
> > Hi, im just wondering has anyone really explored the performance
> > limitations of linux raid ?
> >
> > Recognising ones limitations is the first step to overcomming them.
> >
> > Ive found that relative performance increases are better with less
> > drives.
> >
> > Ive been using raid for a year or so, ive never managed to get a 4-way
> > ide raid working efficiently (no timeouts), 2.3.99pre6pre5 is the best
> > ive had though.
> >
> > Anyone have any thoughts on where the bottleneck is, or orther
> > experiences with raid limitations ?
>
> I've not had any real problems using striped sets of SCSI drives as
> RAID 0 and RAID 5. You're always going to get rather crappy performance
> with lots of IDE drives unless you have only 1 drive per channel. By
> the time you buy that many controllers, the cost is pretty much a
> wash with SCSI.
>
Ive just managed to setup a 4 way ide raid0 that works.
The only way i can get it working is to use *two* drives per channel.
I have to do this as i have concluded that i cannot use both my onboard
hpt366 channels and my pci hpt366 channels together.
Ive done some superficial performance tests using dd, 55MB/s write
12MB/s read, interestingly i did get 42MB/s write using just a 2 way ide
raid0, and got 55MB/s write with one drive per channel on four channels
(i had no problem writing, just reading) so surprisingly i dont think
the drive interface is my bottleneck.
I think read performance is a known problem, but at least i dont get
lockups or timeouts anymore.
IDE will always beat SCSI hands down for price/performance, but scsi is
clearly the winner if you want 4 or more drives on one machine, as ide
just doesnt scale.
SCSI drives are >50% dearer than ide arent they ?
What sort of performance do you get from your scsi sets ?
I wonder what the fastest speed any linux software raid has gotten, it
would be great if the limitation was a hardware limitation i.e. cpu,
(scsi/ide) interface speed, number of (scsi/ide) interfaces, drive
speed. It would be interesting to see how close software raid could get
to its hardware limitations.
Perhaps as a way of advertising/tracking the benefits of linux-raid we
could have a top 10 ranking for each raid mode. Maybe it would help
people to see the performance gains raid can bring.
Glenn McGrath
