ext3 usage guidance

[T. Horsnell]

On Thu, Mar 29, 2007 at 03:16:44AM -0600, Andreas Dilger wrote:
> On Mar 28, 2007  18:47 +0100, T. Horsnell wrote:
> > 1. The effect on performance of large numbers of (generally) small files
> >    One of my ext3 filesystems has 750K files on a 36GB disk, and 
> >    backup with tar takes forever. Even 'find /fs -type f -ls'
> >    to establish ownership of the various files takes some hours.
> >    Are there thresholds for #files-per-directory or #total-files-per-filesystem
> >    beyond which performance degrades rapidly?
> 
> You should enable directory indexing if you have > 5000 file directories,
> then index the directories.  "tune2fs -O dir_index /dev/XXX; e2fsck -fD /dev/XXX"

Thanks very much.
Do you mean '> 5000 directories-per-filesystem' or '> 5000 files-per-directory' ?
tune2fs refers to 'large directories' which implies to me that its files-per-directory

Cheers,
Terry.

> 
> > 2. I have a number of filesystems on SCSI disks which I would
> >    like to fsck on demand, rather than have an unscheduled
> >    fsck at reboot because some mount-count has expired.
> >    I use 'tune2fs -c 0 and -t 0' to do this, and would like
> >    to use 'shutdown -F -r 'at a chosen time to force fsck on
> >    reboot, and I'd then like fsck to do things in parallel.
> >    What are the resources (memory etc) required for parallel
> >    fsck'ing? Can I reasonably expect to be able to fsck say,
> >    50 300GB filesystems in parallel, or should I group them into
> >    smaller groups? How small?
> 
> I think it was at least "(inodes_count * 7 + blocks_count * 3) / 8" per
> filesystem when I last checked, but I don't recall exactly anymore.
> 
> Cheers, Andreas
> --
> Andreas Dilger
> Principal Software Engineer
> Cluster File Systems, Inc.
> 

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