Cyrus IMAP running in linux: recommended file system

[Andre Felipe Machado]

Hello,
We used ext3 for years at cyrus servers (even tuned them a lot [0]), then
changed to XFS **aggressively tuned for small files** [0] and are being happy
with it.
But we are using plenty ram and cores servers and tuned SAN FC storage and now
even a tuned custom WAFL SAN FC storage, with lvm.
At this scenario, XFS parallel concepts shine.
After written the article [0], we adopted the Allocation Group size of 256 MB
for new servers and it increased final performance (approximately our average
user quota) at parallel loads, with good write performance of *small files*.

There is a tricky trade-off between number of AG and cpu load and parallel iops
and cpu i/o contention and file size and write X read profile.

Key details of XFS is that it creates new directories at their own AG when
possible, and has delayed allocation, spreading load and parallelism and
reducing fragmentation. We are not using pre-allocation. Also, an eventual xfs
verify is faster than a ext3 one.
As we use Debian Stable (mostly) and RH (at some legacy email servers soon to be
decomissioned this year) other fs were not considered nor tested for production
deployments.
Currently, we are stress testing a cyrus murder on Debian, on a Xen VMs, using
VHD vdisks, containing a XFS, for comparisons with raw lvm vdisks.

Good luck.
Andre Felipe Machado

[0]
http://www.techforce.com.br/news/linux_blog/lvm_raid_xfs_ext3_tuning_for_small_files_parallel_i_o_on_debian