[linux-lvm] devices.filter changed behaviour in 80ac8f37d6
chris at arachsys.com
Mon Sep 7 13:44:18 UTC 2015
Peter Rajnoha <prajnoha at redhat.com> wrote:
> Yes, without lvmetad daemon, each LVM command needs to run full device
> scan at its start to look for PVs and then when a PV is found, it needs
> to read all LVM metadata it finds (and check for consistency etc etc).
> Of course, not including those devices which are filtered out.
> However, with lvmetad, you can save some disk access here since all the
> metadata are taken from lvmetad cache...
> Lvmetad doesn't have any extra deps except what lvm binary already has.
Sounds like a clear performance win for us. I'll have a play.
> If you're not using udev to handle kernel uevents (hmm, what are you using
Nothing particularly clever or interesting I'm afraid: just a very trivial
daemon which translates events from a NETLINK_KOBJECT_UEVENT socket into a
continuous blocking stream.
This is then consumed by a simple read loop to implement the handful of
rules we actually want.
It'd be easy to add pvscan --cache when the relevant devices appear or
disappear. Thanks for the pointer.
(I note from the pvscan(8) man page that global_filter applies to pvscan
--cache but not standard filter, which sounds like another good reason to
switch to global_filter!)
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