[Dovecot] Documentation clarifiction on mmap_disable

Timo Sirainen tss at iki.fi
Mon Dec 12 14:21:02 EET 2011

On 12.12.2011, at 13.57, Marcio Merlone wrote:

> On http://wiki.dovecot.org/MainConfig I read:
> "mmap_disable = no
>   Don't use mmap() at all. This is required if you store indexes to
>   shared filesystems (NFS or clustered filesystem). "

The wording is a bit too strong, but..:

> Does that mean:
> 1. mmap is required when using NFS or
> 2. it is required to don't use mmap at all when using NFS?

It's better not to use mmap() with NFS.

1. mmap_disable=yes is required if you attempt to access the same mailbox from more than one Dovecot server, otherwise index files get corrupted really easily. But even with this setting this setup isn't safe! http://wiki2.dovecot.org/NFS explains the problems.

2. mmap_disable=yes is a good idea with NFS even if there's only one Dovecot server, since it should be more optimal and also failures are handled better.

3. mmap_disable=yes is a good idea with cluster filesystems, since it should make the performance better.

4. With local filesystems mmap_disable=no should be faster.

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