Thousands concurrent parallel read write accesses over tens of millions of small files is a terrible performance tuning problem for e-mail servers.

You must understand and fine tune all your infrastructure chain, following the previous articles for data storage and multipath on Debian 5.x Lenny.

We reduced the CPU I/O wait from 30% to 0,3% (XFS) and 5% (EXT3) with these combined previously undocumented file system tuning tips.