On Friday 06 May 2016 01:51:34 Timo Sirainen wrote: >On 05 May 2016, at 16:21, Marc Joliet <[email protected]> wrote: >> (Note: I am not subscribed to this ML, so please be sure to CC me in >> replies.) >> >> Hello, >> >> I see a strange bug when running dovecot under btrfs with a mailbox in >> mdbox >> format. At some point, which can take a few minutes or more than a day, >> dovecot starts logging pread() failures, like so: >> >> Apr 02 23:43:42 thetick dovecot[570]: imap(marcec): Error: pread() failed >> with file /home/marcec/.mdbox/mailboxes/LinuxAudio/User/dbox- >> Mails/dovecot.index.log: Input/output error >> >> These would trigger when getmail runs (which in turn is configured to use >> dovecot-lda). It's only ever the *.index.log files, and it would usually >> happen to the same one many times in a row. To demonstrate, this is the >> full >> list of unique pread() failures on one host (my desktop PC): >*.index.log files are always appended to using O_APPEND flag. Maybe this is >relevant. > >Also when a new .log file is created it's opened without the O_APPEND flag >and the O_APPEND is added later. This was causing a bug recently in unionfs, >which ignored the flag change and caused log file corruption.
I will mention that in the btrfs ML thread. Who knows, maybe it will lead to something. >> Rebooting the system would make it go away (without loss of mails), though >> remounting the file system should have worked, too. I tried a variety of >> options, but the only one that helped was to convert the mailbox from mdbox >> to maildir. I have not seen any pread() failures in the two weeks since. >I can't really think of why Maildir format would get rid of the problem, >since the dovecot.index.log files still exist and they're accessed the same >way. Maybe with Maildir there are enough locks that it prevents some race >condition that triggers this. > >You could try stress testing with imaptest to see if it's easy to reproduce: >http://imapwiki.org/ImapTest I will experiment with that when I have some more time. Thanks for the suggestions! Greetings -- Marc Joliet -- "People who think they know everything really annoy those of us who know we don't" - Bjarne Stroustrup
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