On Tue, Dec 02, 2014 at 08:51:40AM +0530, Shriramana Sharma wrote: > On Mon, Dec 1, 2014 at 6:24 AM, Chris Murphy <li...@colorremedies.com> wrote: > >> But isn't it just possible to move i.e. reparent a > >> subvol so I can move these two under another subvol and have that as > >> default? > > > > You can move subvolumes. > > OK so I just found out that just mv test1/foo test2/ where test1, > test2 and foo are all subvolumes is sufficient to reparent foo to > test2, if what btr sub list shows as "top level" is indeed the parent > subvolume. > > Is that correct: what btr sub list shows as "top level" is indeed the > parent subvolume?
No, it's the top-level subvolume. (See my earlier mail about nomenclature). "Parent subvolume" has a number of meanings, none of which should be "the subvolume with subvolid 5". > > My suggestion is subvolumes containing > > binaries shouldn't be located within another subvolume that ends up > > being mounted, that way old binaries with possible vulnerabilities > > aren't exposed in the normal search path. > > I'm not sure what you mean. Are you saying that for example /usr/bin should > be: > > 1) a separate subvolume than / or /usr, > 2) not a child subvolume of / or /usr? > > > openSUSE uses subvol id 5 for installing the OS to, and some > > directories are made subvolumes such as home var and maybe usr. > > Therefore when subvolid 5 is snapshot, those are exempt, and have to > > be individually snapshot. > > Yes I also noticed that openSUSE creates such separate subvols, but is > there any particular benefit to making it so? In the sense of allowing independent snapshotting, yes. I might want to back up / (with usr, var, and so forth) only when I do a system upgrade, but /home every night. Making /home a separate subvol gives me the ability to snapshot those two areas independently. > > Fedora uses subvolumes root and home by default, and fstab uses > > subvol=root and subvol=home to mount them at / and /home respectively. > > This seems similar to Ubuntu's @ and @home setup. > > Is there any advantage to either? That is, one model installs root to > the topmost subvol and makes usr, home etc nested subvols, whereas > another makes root a nested subvol under the topmost just like usr > home etc, and then mounts it to /... > > In general it seems people (or at least distros) prefer avoiding > nesting subvolumes. Is there any particular reason for this? Esp in > regard to /usr etc it would seem that if they are nested within the > subvol for /, then just mounting that subvol would automatically mount > all nested subvolumes, right? So the extra effort needed to mount the > nested subvols would not be necessary, no? Nested subvols tend to get messy in practice. It's harder to replace a "higher level" one, because you've got to move the "lower level" ones around. It's also much harder to make a send/receive backup of the subvols in their original relationships, because of the read-only requirement. Whilst the theory came first, several years of practice has shown both that nesting subvolumes is generally more awkward to manage, and that putting files in the top-level subvol can't do what most people want to do with it. Hence the recommended subvol management layout at [1]. Hugo. [1] https://btrfs.wiki.kernel.org/index.php/SysadminGuide#Subvolumes -- Hugo Mills | We teach people management skills by examining hugo@... carfax.org.uk | characters in Shakespeare. You could look at http://carfax.org.uk/ | Claudius's crisis management techniques, for PGP: 65E74AC0 | example. Richard Smith-Jones, Slings and Arrows
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