[linux-lvm] LVM snapshots and filesystem quiescence

[Les Mikesell]

On Thu, Apr 25, 2013 at 1:35 PM, Tom Coughlan <coughlan at redhat.com> wrote:
>
>> I know that you have to quiesce SQL databases using their own native
>> tools if you want to have a consistent snapshot of the raw db files, but
>> what about other programs like postfix or dovecot that are constantly
>> (on a busy server) writing to disk? Do you need to stop these, take the
>> snapshot, then restart them? Or will the filesystem itself handle this
>> (similar to how VSS works on windows)?
>
> The LVM management tools will automatically suspend the file system
> before taking the snapshot. Refer to the following, from the RHEL 6.4
> Storage Administration Guide:

But having the file system suspended doesn't mean that the files are
in a consistent state from any application's point of view, does it?
Linux fsync() performance has historically been so bad that I would
not expect most applications to use it.

--
  Les Mikesell
    lesmikesell at gmail.com