On Thu, Apr 09, 2015 at 04:27:08PM -0700, Justin Maggard wrote: > On Thu, Apr 9, 2015 at 3:24 PM, Hugo Mills <hugo@xxxxxxxxxxxxx> wrote: > > On Thu, Apr 09, 2015 at 03:01:55PM -0700, Justin Maggard wrote: > >> On Wed, Apr 8, 2015 at 5:45 PM, Qu Wenruo <quwenruo@xxxxxxxxxxxxxx> wrote: > >> > Hi, > >> > > >> > You can use btrfs quota feature to do it. > >> > Like this: > >> > > >> > # btrfs quota enable <MNT_POINT> > >> > # btrfs quota rescan -w <MNT_POINT> > >> > # btrfs qgroup show -prce <MNT_POINT> > >> > qgroupid rfer excl max_rfer max_excl parent child > >> > -------- ---- ---- -------- -------- ------ ----- > >> > 0/5 2248704 12288 0 0 --- --- > >> > 0/256 5509120 3272704 0 0 --- --- > >> > > >> > > >> > rfer is all the space the subvolume takes. > >> > excl is the exclusive space the subvolume takes. > >> > > >> > >> Yes, but this isn't as useful as it sounds if you have more than one > >> snapshot. Because if a file is included in at least two snapshots, > >> it's no longer exclusive. So AFAICT even with btrfs qgroups, you > >> still cannot answer the question "How much space are my snapshots > >> using?" for a given subvolume, unless you have only one snapshot. But > >> I'd be happy to be informed otherwise. :-) > > > > There are basically two useful answers to that question, depending > > on how the question is specified, exactly: > > > > 1) How much space would I use if I copied this subvolume to a > > different filesystem? > > > > 2) How much space would I free up if I deleted this subvolume? > > > > Part 1 is the rfer answer. Part 2 is the excl answer. > > > > Which of these do you mean by "How much space are my snapshots > > using?". The question as posed is highly ambiguous, and needs > > considerably more precision before it can be answered. > > > > If you can pose the question more precisely, you might wish to ask > > one of those questions about N subvolumes as a group -- this is > > where(*) you would define a qgroup covering the subvols you're > > interested in, and then use the above interface to ask the question > > for the group of subvols as a whole. > > To be more precise, let's consider an example, where we have a > subvolume named "stuff"; and two snapshots of "stuff", "snap1" and > "snap2". So the question I'm posing is: > > How much space would I free up if I were to remove my snapshots, > "snap1" and "snap2", but keep "stuff" intact? > > I can't use the rfer value from snap1 and snap2, because in general > most of that space is shared by "stuff" and would not be freed. I > could look at the excl column for snap1 and snap2 and add them up; but > if they shared extents with each other (and not with "stuff"), those > extents are no longer exclusive, and thus not accounted for. So I > would have to delete either snap1 or snap2 in order to answer my > question using qgroups. > > I can't think of a way to define a qgroup that would be able to answer > my question, although I'm admittedly no expert in qgroups either. I think you'd define a qgroup comtaining snap1 and snap2, and look at the excl value. Anyone out there with qgroups experience who can tell us how/whether that would do the job? Hugo. > -Justin > > > > > Hugo. > > > > (*) I'm not an expert in qgroups. I may have the idea completely > > wrong, but I think this is the right kind of approach. > > > > > >> -Justin > >> > >> > You can also refer to 'btrfs-quota'(8) and 'btrfs-qgroup'(8), > >> > Also the following wiki can help: > >> > https://btrfs.wiki.kernel.org/index.php/Quota_support > >> > > >> > NOTE: quota is not so stable and has some problem, but should give > >> > you enough info. > >> > > >> > Thanks, > >> > Qu > >> > > >> >> # zfs list -t snapshot > >> >> NAME USED AVAIL REFER MOUNTPOINT > >> >> hetz0/be0-mail@2015-03-10 2.88G - 387G - > >> >> hetz0/be0-mail@2015-03-11 1.12G - 388G - > >> >> hetz0/be0-mail@2015-03-12 1.11G - 388G - > >> >> hetz0/be0-mail@2015-03-13 1.19G - 388G - > >> >> hetz0/be0-mail@2015-03-14 1.02G - 388G - > >> >> hetz0/be0-mail@2015-03-15 989M - 386G - > >> >> > >> >> Is there any way to do something similar to the above ZFS command? It's > >> >> handy > >> >> to know which snapshots are taking up the most space, especially when > >> >> multiple > >> >> subvols are being snapshotted. > >> >> > > -- Hugo Mills | Great films about cricket: The Third Man hugo@... carfax.org.uk | http://carfax.org.uk/ | PGP: E2AB1DE4 |
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