On Mon, 2009-05-11 at 15:05 +0000, Richard Hobbs wrote: > Hi All, > > We are soon to migrate our mail server from one piece of hardware to > another and we would like to take this opportunity to optimize things. > As a result, we would like to replace "uw-imapd" and "qpopper" with > "dovecot". The version we will be installing is 1.1.13-2, as this is > what is available through the latest Debian stable backports. We will > also be using exim to deliver mail (through dovecot's deliver mechanism, > of course). > > So... We are currently using the mbox format with uw-imapd, and would > like to migrate to the fastest solution possible with dovecot on the new > hardware. My understanding is that "multi-dbox" is not an option in this > version anyway, maildir is OK, but not great, and "single-dbox" is > therefore going to be the highest performing solution. Is single-dbox > the fastest way to go, considering we're going to be using email in the > following ways:
Single-dbox is the highest performing, but note that it's not as much tested as mbox and Maildir code. I think it should work ok, but I'm not aware of any larger installations using dbox currently. So in case you find a problem, you might have to upgrade/patch Dovecot to get it fixed and that would require compiling from sources. > One problem that may arise is the fact that when we migrate, all msg > UIDs will be lost. If i'm not mistaken, this means that all emails will > be treated by the mail client as brand new, and if through IMAP, will > all go bold, and if through POP3, will all be downloaded again (if still > on the server) and therefore duplicated in the mail client. If this is > the case, is there anything we can do to stop this happening? Does the > "Convert" plugin does this job well? mbox -> Maildir conversion can preserve both IMAP and POP3 UIDLs using an external script. Maildir -> dbox conversion can also preserve both, but that causes Dovecot to use this "hybrid Maildir-dbox format", which is slower than the full native dbox. > 8. Configure the "convert" plugin to begin converting the mail to dbox > format. > > 9. Run something manually (if possible) to convert mailboxes before > people connect, so the task is already done by the time the outage is over. There's convert-tool that you could use. I don't know if Debian packages it. > Basically, i suppose i'm asking, with the highest performing mailbox > option, is dovecot going to run faster with 2 individual arrays each > made from 2 disks, or a single 4-disk array (in which case we'd go > RAID > 0+1)? My guess is that two RAID-1s would be faster, but I haven't really done any benchmarking. Anyway index files are 10-30% of the mailbox size, so the index-disks would be using a lot less disk space. > Also... would it be useful to turn off "atime" when we mount the > volume(s) or does dovecot rely on this? Dovecot doesn't rely on atime updates, so turn them off.
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