[295] in linux-scsi channel archive
Re: Slow SCSI - severe performance problems
daemon@ATHENA.MIT.EDU (Drew Eckhardt)
Fri Jun 23 18:48:27 1995
To: Thomas.Koenig@ciw.uni-karlsruhe.de (Thomas Koenig)
cc: linux-scsi@vger.rutgers.edu
In-reply-to: Your message of "Fri, 23 Jun 1995 20:47:27 +0200."
<199506231847.UAA00418@mvmampc66.ciw.uni-karlsruhe.de>
Date: Fri, 23 Jun 1995 16:06:31 MDT
From: Drew Eckhardt <drew@boulder.openware.com>
In message <199506231847.UAA00418@mvmampc66.ciw.uni-karlsruhe.de>, Thomas.Koeni
g@ciw.uni-karlsruhe.de writes:
>We've recently bought an optical SCSI disk for backups (for Macs,
>originally, but why not use it for Linux, as well?). This disk
>is relatively slow, 550 kb/sec reading from the raw device.
>
>We've got this device, a IBM 0632CHX (SCSI ID 4), hanging off a Seagate
>ST31200N (SCSI ID 2), which in turn hangs off a NCR53c810.
>
>When doing heavy disk I/O (such as writing a 60 - megabyte file and
>rereading it, using iozone), the whole machine becomes very, very
>sluggish whenever disk I/O is required; it locks up for minutes on end
>until the iozone command is finished. Needless to say, this makes the
>whole optical disk rather useless for day-to-day use.
>
>Everything's deteced correctly at boot time.
>
>Ideas?
Disconnect/reconnect. Namely, a lack thereof. Combine that with the NCR's
allowance for large data transfers (we currently allow 127 scatter gather
segments), a slow device, and the fairness in scheduling problem you end up
with in this case (lots of requests for the slow device will pile up and
need to finish before you can access your other drives and you may be locked
out of your disk for a couple seconds at a time.
We may want to address this fairness issue, but it is a moot point
with more reasonable device drivers.
I just upgraded my system to 1.2.10, GCC 2.6.3, modules 1.2.8, and moved
all my partitions onto a fat EIDE drive, and started poking at things
again.
Today, management killed my C++ debugger at work, so I won't be burned out
on hacking things here, might be able to play with Linux full time for a
while after I'm gone in a month :-)
