[Dovecot] ext3/ext4 performance issue

[Seth Mattinen]

Matthijs Kooijman wrote:
> Hi Scott,
> 
>> One could always run the mailstore on LVM and then you could snapshot the
>> mount and then fsck it while still technically in use. It would probably slow
>> down the filesystem, but it is still live.
> Uhm, and then you have a nice and fsck'd snapshot, but your live filesystem
> will still be untouched? Or do you propose replacing the mailstore with a
> (readonly?) versioned mounted from the lvm snapshot? I'm not aware of anything
> that can swap filesystems like this online (ie, with files open) and that
> would also mean that while fsck'ing, you can only read mail, not receive, move
> or delete mail?
> 

Changes made to a snapshot will never been seen by the fs it was
snapshotted from and vice-versa. It uses copy on write which will get
progressively slower as the snapshot and the origional diverge until you
end up with a performance disaster.

http://www.nikhef.nl/~dennisvd/lvmcrap.html

~Seth