Subject: Re: Strange system behaviour when copying disks
From: Olaf =?iso-8859-2?Q?Fr=B1czyk?= <olaf@cbk.poznan.pl>
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Date: 15 May 2003 15:35:05 +0200
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On Wed, 2003-05-14 at 14:53, Olaf Frączyk wrote:
(...)
> If I copy disk /dev/hda to /dev/hdc:
> cat /dev/hda > /dev/hdc the system becomes __highly__ unresponsive
> Processor is about 90 % idle
> Load average is about 5
> Working with X is impossible (about 1 second freeze every 1-2 seconds).
> As the root partition is also XFS I have no possibility to load vanilla
> kernel and try with it. I also have no free partition on SCSI disk to
> install fresh system with vanilla kernel for testing.
> renice -19 for X makes no difference.
Hi,

I just repartitioned my SCSI disks and got 2GB free.
I installed RH 9 with Gnome. It took only about 1.6GB :)

So:
With RedHat 2.4.20-8 kernel it is much better. But it still has some
freezes. Load is about 4, CPU is about 90% idle. 'cat' takes about 3-5 %
CPU.

With vanilla 2.4.20 it is the same as 2.4.20 with XFS. Load is about 5,
CPU is about 90% idle. 'cat' takes about 3-5 % CPU.

What is really strange, if I use 'dd' eg.:
dd if=/dev/hda1 of=/dev/hdc1 bsize=1024 count=1000000
there are NO freezes at all.
The system works smoothly. Load is about 1.2.
dd takes for some time 30% CPU and then until finishes about 0.2 % CPU.
This is for radhat, vanilla and vanilla+XFS kernels.

So it is not caused by XFS code. I'll take it to LKML.

BTW, does somebody know why there is such strange difference between
doing 'dd' and 'cat'?

The copy speed is the same for 'dd' and 'cat': about 6.6 MB/sec

Regards,

Olaf