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ext3 instability in RH8.0?



We've been noticing some problems with ext3 and, in our
case, postfix, that appear to come to light under heavy
disk i/o loading.  A previous thread found here
(http://www.redhat.com/mailing-lists/ext3-users/msg04189.html)
documents an identical set of symptons (and similar setup),
but with RH 7.2

The specifics are this:

  1. Stock install of RH8.0 with postfix.
  2. Linux mx 2.4.18-14 #1 date i686 i686 i386 GNU/Linux
  3. Email list delivery to ~40,000 recipients, each with
     their own customized msg. (In other words, these are
     40K unique messages going out, not one msg to
     40K unique recipients).
  4. Postfix parameters (processes) and system resources
     such that no file swapping occurs. (1 Gig processor,
     80 Gig 7200 RPM drives, 1 Gig RAM)

7 distinct processes on another system start firing off as
fast as they can email to this system which then deilivers
it as necessary to other mx servers.

The results are interesting:

1. Very quickly while running "vmstat", one will see decent
   "bo" activity corresponding to the acceptance of the
   various messages, and context switches in the neighbourhood
   of 30-40,000 per second.

2. After about 10-15 seconds, "bo" activity drops to ZERO, and
   context switching ramps up to about 1,000,000 per second.
   After a while, the context switches drop back down, and we're
   back to seeing heavy "bo" activity.

3. After cycling through the behaviour in step 2 several times,
   (after 3-4K msgs are delivered), the context switching remains
   high, and "bo" activity remains at zero.

4. Examining the system with "top" shows a huge run queue - all
   smtp processes are running full tilt.

This above set of conditions were repeated numerous times after
reboots.

Finally, taking the heavily used disk partition (/var) and
setting it to ext2 and rebooting and resuming mail delivery,
absolutely NO problems occur.

To summarize: the mail configuration works in an old RH6.2
setup, in RH8.0 with ext2, but makes the system unusable
with RH8.0 with ext3.

On numerous other non-heavily loaded systems, we've never
had problems with ext3 (all RH8.0 base).

Cheers, Thomas





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