archive mirror
 help / color / mirror / Atom feed
From: Tom Sightler <>
To: Mark Hahn <>
Cc: Linux-Kernel <>
Subject: Re: 2.4.6-pre2, pre3 VM Behavior
Date: Wed, 13 Jun 2001 22:08:17 -0400 (EDT)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>
In-Reply-To: <>

Quoting Mark Hahn <>:

> > 1.  Transfer of the first 100-150MB is very fast (9.8MB/sec via 100Mb
> Ethernet,
> > close to wire speed).  At this point Linux has yet to write the first
> byte to
> > disk.  OK, this might be an exaggerated, but very little disk activity
> has
> > occured on my laptop.
> right.  it could be that the VM scheduling stuff needs some way to
> tell
> whether the IO system is idle.  that is, if there's no contention for 
> the disk, it might as well be less lazy about writebacks.

That's exactly the way it seems.

> > 2.  Suddenly it's as if Linux says, "Damn, I've got a lot of data to
> flush,
> > maybe I should do that" then the hard drive light comes on solid for
> several
> > seconds.  During this time the ftp transfer drops to about 1/5 of the
> original
> > speed.
> such a dramatic change could be the result of IDE misconfiguration;
> is it safe to assume you have DMA or UDMA enabled?

Yes, UDMA/33 is enabled and working on the drive (using hdparm -d 0 makes the
problem way worse and my drive performs about 1/4 the speed).

> > This was much less noticeable on a server with a much faster SCSI hard
> disk
> > subsystem as it took significantly less time to flush the information
> to the
> is the SCSI disk actually faster (unlikley, for modern disks), or 
> is the SCSI controller simply busmastering, like DMA/UDMA IDE,
> but wholly unlike PIO-mode IDE?

First, lets be fair, we're comparing a UDMA/33 IDE drive in a 1 year old laptop
(IBM Travelstar, if your interested) to a true SCSI Disk Subsystem with
mirrored/striped Ultra160 SCSI disk connected via 64bit PCI/66Mhz bus, so yes,
the SCSI subsystem is MUCH faster.  Specific numbers:

Laptop with TravelStar IDE HD Max sustained read: 16.5MB/s
Server with Ultra160 SCSI disk array Max sustained read: >100MB/s

That's a big difference.  The Travelstar is probably only 5400RPM and is
optimized for power savings, not speed, the SCSI subsystem has multiple 15000RPM
in a striped/mirrored configuration for speed.


       reply	other threads:[~2001-06-14  2:08 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2001-06-14  2:08 ` Tom Sightler [this message]
2001-06-13 19:31 2.4.6-pre2, pre3 VM Behavior Tom Sightler
2001-06-13 20:21 ` Rik van Riel
2001-06-14  1:49   ` Tom Sightler
2001-06-14  3:16     ` Rik van Riel
2001-06-14  7:59       ` Laramie Leavitt
2001-06-14  9:24         ` Helge Hafting
2001-06-14 17:38           ` Mark Hahn
2001-06-15  8:27             ` Helge Hafting
2001-06-14  8:47       ` Daniel Phillips
2001-06-14 20:23         ` Roger Larsson
2001-06-15  6:04           ` Mike Galbraith
2001-06-14 20:39         ` John Stoffel
2001-06-14 20:51           ` Rik van Riel
2001-06-14 21:33           ` John Stoffel
2001-06-14 22:23             ` Rik van Riel
2001-06-14 15:10       ` John Stoffel
2001-06-14 18:25         ` Daniel Phillips
2001-06-14  8:30   ` Mike Galbraith

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).