You don't really *have* to stop I/O. In fact, I recommend you don't unless you have to.
The reason why this is recommended is to minimize the risk of data loss because the snapshot will be in a very similiar state as if you suddenly lost power to the server. Obviously if you need to have the same state of data in the snapshot (and we're talking about rollback of several seconds typically). For example if you append some data to a file and do a snapshot instantly the data will likely not be there (yet). The reason why I recommend you don't do that is because this exposes problems with data consistency in the guest (applications/developers doing something stupid...) which is a good thing! If you suddenly lose power to your production database, you don't want to have to restore from backup. In an ACID compliant database all the data should simply be there no matter how harsh the shutdown was. So unless you deliberately run your guests with disabled barriers/flushes*, or you need the absolute latest data, don't bother quiescing IO. * in which case there's no guarantee even with fsfreeze Jan > On 09 Dec 2015, at 03:59, Yan, Zheng <uker...@gmail.com> wrote: > > On Wed, Dec 9, 2015 at 12:10 AM, Dan Nica <dan.n...@staff.bluematrix.com> > wrote: >> Hi guys, >> >> >> >> So from documentation I must stop the I/O before taking rbd snapshots, how >> do I do that or what does that mean ? do I have to unmount >> > > see fsfreeze(8) command > > >> the rbd image ? >> >> >> >> -- >> >> Dan >> >> >> _______________________________________________ >> ceph-users mailing list >> ceph-users@lists.ceph.com >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >> > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
