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Re: ext3/kjournald overhead



Carlos Knowlton wrote:
> 
> Hi,
> 
> I've recently installed ext3 on an 800MB RAID5
> (software) array.  I am running RedHat Linux 7.1 with
> the Linux kernel 2.4.12-ac3 on a 1GHz Pentium system
> with 128MB RAM.  I am seeing a significant amount of
> write operation slowdown when running ext3 (and
> kjournald), as opposed to my old ext2.  The problem
> seems to be associated with the times that kjournald
> is accessing the disk.  At those moments, my CPU
> utilization peaks, and network transfer is nearly
> halted until kjournald is finished.
> 

800 megabytes?  That small?

I'll assume that you're using the default journalling
mode.

It could be the return of the RAID5 doldrums. Would it be possible for
you to retest with a Linus kernel?  Say, 2.4.14+ext3?

If the problem remains then could you please additionally try this patch:

http://www.kernel.org/pub/linux/kernel/people/andrea/kernels/v2.4/2.4.14pre7aa2/00_lowlatency-fixes-2

Also, please tell us what `top' and `ps' are saying about
kjournald CPU utilisation.

A `vmstat 1' trace during heavy write traffic would be interesting
as well.

Thanks.





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