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Re: Ext3 on RAID5 for video archive server


On Wed, 2003-12-17 at 15:06, M K wrote:

>   Still, I keep getting "hiccups" every few seconds while writing the
> files.. mostly, these hiccups are at 5-second intervals, so it may
> suggest that the ext3 default commit interval is the culprit, and the
> effect has diminished after i changed the commit interval to 1 second
> in the kernel code, under 
> linux/fs/jbd/journal.c, the line changed was:
> journal->j_commit_interval = (HZ * 1); // originally HZ * 5.

>     I have some questions at this point:
> 1. Is there any other way of modifying the commit interval? If
> possible I would like to take the commit interval modification out of
> the kernel and put it back in user level code.. 

Yes, you can mount with "-o commit=1" (or put "commit=1" in the options
field in /etc/fstab) as long as you've got a moderately recent kernel. 
The 2.4.20-20.* Red Hat Linux kernels should include that.

> 2. Are there other things that I should try to optimize the write
> performance?

There are various things you could try.  In general, avoiding
dependencies between different IOs is a good thing.  That can mean
splitting up files amongst more directories (htree will help to avoid
the cost of large dirs, of course); or even splitting the storage into
multiple different filesystems, or splitting the raid array into
multiple arrays.  Really, though, it's so application-dependent that
it's hard to be any more specific than this.


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