ext3 usage guidance

T. Horsnell tsh at mrc-lmb.cam.ac.uk
Wed Mar 28 17:47:32 UTC 2007

Is there a document anywhere offering guidance on the optimum
use of ext3 filesystems? Googling shows nothing useful and the
Linux ext3 FAQ is not very forthcoming.

I'm particularly interested in:

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?

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?



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