On Mon, Jan 27, 2014 at 11:35:03AM -0700, Chris Murphy wrote: > > On Jan 27, 2014, at 7:03 AM, Hugo Mills <hugo@xxxxxxxxxxxxx> wrote: > > > On Mon, Jan 27, 2014 at 02:53:36PM +0100, KC wrote: > >> I have been trying to understand how snapshots work (in BRTFS and in > >> general), but I still have some questions, and would appreciate if > >> someone could clear them for me. > >> To make things easier, I tried to make most of them Yes/No questions: > >> > >> 1. When creating the filesystem, I only made btrfs partition with no > >> subvolumes. Do I have to use subvolumes, or can I snapshot entire > >> “/“? > > > > / (the top level of the FS) is a subvolume as well -- it's the only > > one that can't be renamed or deleted, though. > > > I'll point out a source of confusion I've had, and see new users have the same confusion quite often also. Within the file system hierarchy, / is a mount point. It could be that subvolume ID 5 is mounted there, which is how opensuse's default rootfs on Btrfs works. However, Fedora's / is a subvolume named root, the top level ID 5 subvolume isn't mounted by default. I agree the terminology gets confusing. I try to be consistent with the set of words used in the SysadminGuide and (at least some of) the rest of the website: Subvolume id=5: "top level of the FS" The top of the current visible UNIX filesystem structure: "/" Root's home directory: "~root" I always try to avoid using the word "root" for any of them, as it's rather heavily overloaded at this point. > So / is not necessarily the top level of the file system. I'm not sure what to call the undeleteable ID 5 subvolume. It's the default subvolume, but if the user changes the default subvolume then it isn't. Calling it the default default is maybe more confusing. And calling it subvolume ID 5 is a bit confusing because subvolume ID 0 maps to 5, and many users are more familiar with subvol ID 0 than ID 5. And then if I have a subvolume within a subvolume mounted and do a btrfs list, it shows top level ID with a value other than 5. > > Anyway I really don't know what else to call the undeletable first subvolume. I call it "the top level of the btrfs filesystem", as that's what it is. (Even if you don't always mount the top level of the FS). Hugo. -- === Hugo Mills: hugo@... carfax.org.uk | darksatanic.net | lug.org.uk === PGP key: 65E74AC0 from wwwkeys.eu.pgp.net or http://www.carfax.org.uk --- I always felt that as a C programmer, I --- was becoming typecast.
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