On Mon, Sep 05, 2011 at 12:13:25PM +0200, Björn Kalkbrenner wrote: > Hi, > > i've got an interesting btrfs subvolume problem which i can't > understand... Maybe someone here can give me a tip because i think > that's only a user error... > > I had a root btrfs on / and made a subvolume some month ago for my home > on /home (i think cwd was / and i used "btrfs subvolume create /home"). > > On friday i wanted to try an update of my distribution, so i > created a snapshot on /snapshots/20110902 (cwd was / and i entered > "btrfs subvolume snapshot / /snapshots/20110902). > > Today i realized that my update failed, so i did > "btrfs set-default 257 /" (257 is the id of the snapshot from friday)... > > When i rebooted, the trouble began. The mounted "home" subvolume was > empty (even if mounted) and the new root from today which i used before > trying the set-default seems to be lost. Ok, not the main problem...
The original root is available by mounting with "subvolid=0" as a mount option. Snapshots do not recurse into snapshots, so when you took a snapshot of your original / (at the top level), you will have got a snapshot of everything within / *except* /home (which is a subvolume). /home should still be available as subvol=/home, or as subvolid=256. > The snapshot from friday was mounted correctly on boot as root. > > The directory /snapshots/20110902 is empty but it is still listed as > subvolume. My "home" was also empty but still listed as subvolume. > I tried to remove the subvolume, i tried to remove the directory, both > not working. The directory you refer to is just a directory at this point, since it's the copy inside /snapshots/20110902. Anything else would be somewhat insane, as you'd have a directory/snapshot loop. The subvolume path it's referring to is not from your currently-mounted /, but is instead from the (currently invisible) top-level directory of your btrfs filesystem, which is only reachable if you mount your filesystem somewhere with subvolid=0. > Then i tried to > "mount -o subvolumeid=256 /dev/mapper/root /home" (id of home subvol) > and the content of my home is back... > > > My questions are: > > 1. where is the "original" root from today morning before i did > set-default? Lost? subvolid=0 > 2. why can't i do "mount -o subvolume=home /dev/mapper/root /home" > anymore? To be more exact, i can, but why is it empty and why is it > working when i enter the subvolume id? I don't know about this one, sorry. > 3. I am now using the snapshot /snapshots/20110902 but what is > /snapshots/20110902 now and why is it still listed? It's empty? It's an empty directory. > 4. can i now delete the snapshots/20110902 or will that drop my current > active working root? The latter -- it will drop your working root. > 5. can i rename snapshots, e.g. the snapshots/20110902 or "home" to > "home-20110905"? I believe that "mv" will accomplish this. > 6. is my btrfs filesystem broken now and should i recreate the whole > thing or is it safe to use it? It sounds like it's all working correctly, and there's nothing wrong. (Well, bar the inability to mount with "subvol=home") Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 515C238D from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- If it's December 1941 in Casablanca, what time is it --- in New York?
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