On 04/10/2015 07:39 AM, Hugo Mills wrote:
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.
Agreed, This is a possible method to get what you want. We can create a
qgroup
in a higher level, as a pool.
# btrfs qgroup create 1/0 /MNT
And then assign your snapshots into this qgroup.
# btrfs qgroup assign 0/xxx 1/0 /MNT
# btrfs qgroup assign 0/xxx 1/0 /MNT
*Considering we can not update the quota number automatically in moving
qgroup
we need a rescan here.
# btrfs quota rescan -w /MNT
Then you can get the information you want by
#btrfs qgroup show -prce /MNT
Thanx
Yang
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.
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
