pread() failures when using mdbox on btrfs

[Marc Joliet]

Am Friday 27 May 2016
schrieb Timo Sirainen <tss at iki.fi>

>On 05 May 2016, at 16:21, Marc Joliet <marcec at gmx.de> wrote:
[...]
>> 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.

Yeah, I was somewhat surprised even without knowing that.  And what do you 
know: two days ago I discovered pread() failures in my system log again, but 
this time they went away by themselves without me noticing that they even 
occurred:

Mai 23 18:03:45 diefledermaus dovecot[600]: imap(marcec): Error: pread() 
failed with file /home/marcec/.maildir/.LinuxAudio.Dev/dovecot.index.log: 
Input/output error
Mai 23 18:03:45 diefledermaus dovecot[600]: imap(marcec): Error: pread() 
failed with file /home/marcec/.maildir/.LinuxAudio.Dev/dovecot.index.log: 
Input/output error
Mai 23 18:13:57 diefledermaus dovecot[600]: imap(marcec): Error: pread() 
failed with file /home/marcec/.maildir/.LinuxAudio.Dev/dovecot.index.log: 
Input/output error
Mai 23 18:13:57 diefledermaus dovecot[600]: imap(marcec): Error: pread() 
failed with file /home/marcec/.maildir/.LinuxAudio.Dev/dovecot.index.log: 
Input/output error

There were also a whole bunch affecting the same file on May 20th, but not 
before.  I probably didn't notice those because they started shortly before I 
rebooted for a kernel upgrade (from gentoo-sources 4.4.10 to 4.5.5).

>You could try stress testing with imaptest to see if it's easy to reproduce:
>http://imapwiki.org/ImapTest

I still haven't had time to do this, but haven't forgotten!

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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