On Tue, 17 Aug 1999, Chance Reschke wrote:
> On Fri, 13 Aug 1999, James Manning wrote:
>
> To be honest, I'm still a little confused that I can't seem to find
> any s/w h/w combination that will yield better than 30MB/sec
> writes to 20 drives (18.2GB Cheetah-3's operating over 2 channels,
> both at 80MB/sec with LVD). Any tips? s/w raid stripe size
> should be (# of h/w raids) * (h/w raid stripe size)? or should
> it be (# of physical drives) * (h/w raid stripe size)?
>
> a cheetah can transfer about ~16-18MB sustained.
>
> so you really don't want more than 4 drives per channel or you'll
> start to lose out. And that's ignoring the overhead of 4 very active
> (under RAID) drives on one bus.
On an Intel architecture machine you'll never get more than about 80MBs
regardless of the number of SCSI busses or the speed of the disks. The
PCI bus becomes a bottleneck at this point.
Another consideration of course. But I think his problem was that he
couldn't get any higher than 30MB/s, let alone 80. :)
What about 64bit PCI? A lot of Intel, Compaq, Dell and Alpha boards
have those slots, and intraserver for one has 64bit PCI scsi
controllers. Then there's the even rarer 66MHz PCI. Wonder how they
would affect the benchmarks.
I missed the start of this thread, so I don't know what RAID level you're
using. I did some RAID-0 tests with the new Linux RAID code back in March
on a dual 450Mhz Xeon box. Throughput on a single LVD bus appears to peak
at about 55MBs - you can get 90% of this with four 7,200RPM Baracudas.
With two LVD busses, write performance peaks at just over 70MBs
(diminishing returns after six disks)
which ties in with why james only sees 30MB/s - 10 drives per
channel.
and reads at just under 80MBs with
eight disks. More disks, more SCSI busses, whatever - the performance
doesn't improve.
regards,
--
Paul Jakma
[EMAIL PROTECTED] http://hibernia.clubi.ie
PGP5 key: http://www.clubi.ie/jakma/publickey.txt
-------------------------------------------
Fortune:
In defeat, unbeatable; in victory, unbearable.
-- W. Churchill, on General Montgomery
