[Dovecot] Dovecot performance issues with many writes

[Andy Robbins]

We are currently experiencing performance issue with our Dovecot system
which we believe is caused by excessive writes to the dovecot files. The
confusing thing is that we are seeing more writes than reads on our Dovecot
volume when you would assume that most of the IO should be reads from
customers checking their mail.

We're seeing reads vs. writes similar to the following:

# iostat -d 5 -x
Device:         rrqm/s   wrqm/s     r/s     w/s   rsec/s   wsec/s avgrq-sz
avgqu-sz   await  svctm  %util
dm-4              0.00     0.00  485.80  865.80  3886.40  6926.40
8.00    28.69   19.63   0.70  94.00
drbd0             0.00     0.00  485.80  865.80  3886.40  6926.40
8.00   111.42   94.44   0.74  99.60

We can't figure out why we would be seeing twice as many writes as we are
reads. Could this have something to do with the index files?

Appreciate any assistance on this issue.