Date: Sat, 1 Jun 1996 14:34:02 +0100 From: Robin Melville <robmel@nadt.org.uk> To: questions@freebsd.org Subject: Agonisingly slow SCSI (was: excessive interrupts) Message-ID: <199606011334.OAA03130@charlie.nadt.org.uk>
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Dear FreeBSD Folks,
I have installed the CD FreeBSD 2.1 release on an HP NetServer LM. This is a
P90 with 16Mb and a 2033Mb HD driven by an HP-hacked on-board Adaptec 7770.
Although it works, disk accesses are agonisingly slow -- eg. kernel
recompiles taking 10x as long as on a 486/33 with WD drives.
My previous posting on this issue (re excessive interrupts) was a red
herring caused by a quirk in xperfmon++.
Running "bonnie" on this host and on a 16Mb PCI-based P90 with non-SCSI
drive shows the following comparison:
**** BENCHMARK RESULTS (bonnie) ****
** Hewlett Packard NetServer LM **
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
100 136 0.0 1824 0.0 582 0.0 149 0.0 1411 0.0 40.7 0.0
** PCI Host **
-------Sequential Output-------- ---Sequential Input-- --Random--
-Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks---
MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU
100 1452 40.5 2122 12.6 824 7.5 1329 36.3 1896 10.0 59.9 3.7
These results seem to show that the per-char throughput on read and write on
the SCSI machine is only 10% of that on the PCI.
I've tried these benchmarks with both a GENERIC and host-specific kernel
with comparable results. The benchmarks were carried out with other SCSI
devices disconnected and the network card removed.
Clearly, since this machine is intended as an NFS fileserver, this kind of
performance is hopeless.
Hope you can help me!
Many thanks,
Robin.
----------------------------------------------------------------------------
Robin Melville
Addiction Information Service
Nottingham Alcohol & Drug Team
Vox +44 (0)115 952 9478 Fax +44 (0)115 952 9421
Email robmel@nadt.org.uk
WWW http://www.innotts.co.uk/nadt/
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