[Dovecot] extremely slow delete/move operations?

[Gregory K. Ruiz-Ade]

I've been working to migrate several hundered users on to our new mail 
servers, which run dovecot 0.99.11 (RHEL4).  The problem I'm seeing is that 
deleting or moving a message seems to take a very long time.  It's not 
uncommon for Thundirbird (1.0.7) to have delays of 5-10 seconds to delete a 
single message from my Inbox (<500k) and place it in my Trash folder (~100MB 
right now).

The systems are Dell PowerEdge 1850 (dual 3.6GHz Xeon) with two 300GB SCSI 
drives in a hardware mirror.  Filesystems are ext3 on LVM.  Inboxes are on 
/var/spool/mail (/export/mail, symlinked into /var).  User mail folders are 
in their home directories (/export/homes1/<user>, automounted to 
/home/<user>; some home directories are NFS automounted from a NetApp). 
Both the mail spool and home directories are available over NFS for 
compatibility reasons with the former setup.

What's really bugging me is that I've used the same software (RHEL4 and 
dovecot 0.9x.x) at my last workplace, and the performance was outstanding; 
it beat UWIMAPd hands-down, especially with large mailboxes.  Here, the 
opposite seems to be true.  The primary difference seems to be that we're 
using NFS here, but I wasn't using NFS at my last job.

I'm getting a lot of grief over the delays when users delete mail or move 
mail from their inbox to one of their mail folders.  Enough so that they're 
now resisting moving to the new server.

Where do I look to find out what's causing the slowness?  What can I do to 
make it faster?

Mailbox formats are mbox.

Using these options in /etc/dovecot.conf:

-----
protocols = imaps pop3s
imap_listen = [::]
pop3_listen = [::]
ssl_cert_file = /usr/share/ssl/certs/csefast.ucsd.edu_cert.pem
ssl_key_file = /usr/share/ssl/private/csefast.ucsd.edu_key.pem
login_dir = /var/run/dovecot-login
login = imap
login = pop3
verbose_proctitle = yes
first_valid_uid = 100
default_mail_env = mbox:~/:INBOX=/var/mail/%u
mail_full_filesystem_access = yes
mbox_locks = dotlock fcntl
auth = default
auth_mechanisms = plain
auth_userdb = passwd
auth_passdb = pam
auth_user = root
-----


Thanks in advance,

Gregory

-- 
Gregory K. Ruiz-Ade
Sr. Systems Administrator
Computer Science and Engineering
University of California, San Diego
Office: EBU3b 1216
Phone:  (858) 822-2625
E-mail: gkra at ucsd.edu