On Thu, 16.07.15 12:40, Chris Murphy ([email protected]) wrote: > Resurrection of related thread "systemd and nested Btrfs subvolumes" from > March: > http://lists.freedesktop.org/archives/systemd-devel/2015-March/029666.html > > The question: > I understand the argument for subvolumes for containers below > /var/lib/machines. I don't understand what feature(s) of Btrfs > subvolumes will be leveraged for /var/lib/machines itself, and why it > isn't just a regular directory that then contains whatever subvolumes > are needed?
so that you can apply quota not only on the individual containers, but on them all together, as well as query disk usage of the all summed up. > The problem: > On openSUSE, it uses subvolumes at the top level of the file system > (in subvolid 5) to make certain things exempt from snapshotting and > rollback: like logs, mail, bootloader, and system settings. See the > fstab in the above URL to see the listing. > > The fstab containing that long list of subvolumes to mount ensures > that those identical subvolumes are always used no matter what > subvol/snapshot the user rollsback to. > > But there isn't an fstab entry for /var/lib/machines. So a.) it won't > get snapshot by snapper and b.) if a rollback is done, the backing > subvolume containing all the nspawn container subvolumes won't be > mounted, it will be empty. > > The solution: > The implied fix for this is to create the subvolume > <FS_TREE>/var/lib/machines at installation time, and add it to fstab > to always mount at /var/lib/machines (a directory found in all > snapshots of /). > https://features.opensuse.org/319287 > > As a consequence, it means if there's a rollback, it's not possible to > delete /var/lib/machines - its contents can be deleted but a mounted > subvolume can't be. > > Hence the question, rephrased, does systemd expect /var/lib/machines > to be an actual subvolume rather than a mountpoint backed by a mounted > subvolume? No. it can be anything. systemd will create it as subvol if it is missing, and you will get more features if it is a subvolume (like the quota/disk usage stuff menionted above) but it degrades gracefully if it is just a normal dir. Lennart -- Lennart Poettering, Red Hat _______________________________________________ systemd-devel mailing list [email protected] http://lists.freedesktop.org/mailman/listinfo/systemd-devel
