too many files in a directory

[Ross Boylan]

My Cyrus 2.2.13 server (Debian stable) is running on an ext3 
filesystem.  One folder contains so many files that it keeps exceeding 
the limit ext3 can cope with (or at least, more than the directory index 
can handle).  I've been able to recover with e2fsck (I don't know if it 
rebalances the tree or makes more room), but clearly need to do 
something else.

I have a narrow question and a broader one.  Narrowly, if I create some 
other folders and move some of the messages into them, will it help?  My 
understanding is that cyrus tries to avoid copying or moving message 
files around on disk, and so I suspect the files will continue to take 
up space in the original directory even if I move them.

More broadly, any other suggestions for dealing with this situation?  
I'm also having very slow backup times, I think the result of the long 
time it takes to traverse the directory.  I might go to reiser3, which I 
used successfully on a different system.  I thought the reiser file 
system seemed like a bad long-term bet after the architect was jailed 
for murder.  But I see from the archives that people are still using it 
and having good experiences.

Thanks for any advice.
Ross

P.S. For the record, the failures do not lose any messages; they result 
in messages going to my main inbox when there's an error on attempted 
delivery to the subfolder.