Date:         Sat, 1 Feb 2003 10:31:31 -0500
Reply-To:     "F.J. Kelley" <jkelley@ARCHES.UGA.EDU>
Sender:       "SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>
From:         "F.J. Kelley" <jkelley@ARCHES.UGA.EDU>
Subject:      Linux Question: Poor filesystem with SAS (fwd)
Comments: cc: Ignacy Misztal <ignacy@arches.uga.edu>
Content-Type: TEXT/PLAIN; charset=US-ASCII

One of our faculty members has sent this question to a local Linux group
and cc'd me.  I am forwarding this to the 'L (and cc-ing him), as I
suspect others will have seen this, and may have an answer to it.  Of
course, this could really be a hardware or OS problem, and SAS is involved
only to the extent that WORK files push the limits.
I believe the machine is a Dell of very recent vintage (not an old p-90
found in the corner)

from his note:

  The system is RH 7.1 with kernel 2.4.17 and has 5x18Gbyte SCSI RAID-5 as
  ext2. A newer system with ext3 filesystem and RH7.5 shows the same
  problem.

Thanks,
--Joe


---------- Forwarded message ----------
Date: Fri, 31 Jan 2003 10:32:35 -0500
Cc: jkelley@uga.edu
Subject: Poor filesystem with SAS

We run SAS on a 4-proc Linux with 2 Gbyte RAM. Our jobs use large
datasets, and SAS creates many temporary files. Once SAS starts running,
the system may be unresponsive for many seconds! Joe Kelley from UCNS
contacted SAS and got a patch. This helped but only partially.

The problem seems to be due filesystem saturation  wrote a small program
that writes many 10 Mbytes files. The first few files get written very
quickly. After some 20 files, the performance drops drastically and the
system seems to lock for 5-60 seconds. I saw a web page where someone
presented Linux as failing under high I/O load.

The system is RH 7.1 with kernel 2.4.17 and has 5x18Gbyte SCSI RAID-5 as
ext2. A newer system with ext3 filesystem and RH7.5 shows the same problem.

Is there any solution to a slow filesystem under RH?