Reducing ZFS blocksize to improve Cyrus write performance ?

[Vincent Fox]

For what Cyrus is doing on Solaris with ZFS, the
recordsize seems nearly negligible.  What with all the
caching in the way, and how ZFS orders transactions, it's
about the last tuneable I'd worry about.

Here's what works well for us, add this to /etc/system:

* Turn off ZFS cache flushing
set zfs:zfs_nocacheflush = 1
* Increase DNLC (Directory Name Lookup Cache)
set ncsize = 500000

Turn off atime of course.

Turn on LZJB compression for metapartition but gzip for
the mail data filesystem. Our compression ratio on the mail
filesystem is showing 1.68x.

Our I/O channels average only 4-5% busy with ~6,000 users
per backed mailstore.  We run nightly snapshots and then
backup every other night from the most recent snapshot and
that is factored into the iostat number.