snapshot strange behaviour

snapshot strange behaviour

[Lubos Kolouch]

Hello,

During doing backups I found strange behaviour... 2.6.37, latest btrfs-
progs from git

nbgentoo ~ # btrfs subv crea a
Create subvolume './a'
nbgentoo ~ # cd a
nbgentoo a # btrfs subv crea b
Create subvolume './b'
nbgentoo a # touch b/file
nbgentoo a # ls -l b/
total 0
-rw-r--r-- 1 root root 0 Jan 23 08:14 file
nbgentoo a # cd ..
nbgentoo ~ # btrfs subv snap a x
Create a snapshot of 'a' in './x'
nbgentoo ~ # ls -l x/b/
total 0

and also

nbgentoo ~ # cd x/
nbgentoo x # btrfs subv dele b 
ERROR: 'b' is not a subvolume

Is this a bug or intended behaviour and I am missing something something?
How to snapshot a subvolume, containing another subvolumes?

(I create subvolume backup, under this another subvolumes as not always I 
want to snapshot the whole backup subvolume).

Thank you

Lubos

Re: snapshot strange behaviour

[Goffredo Baroncelli]

Hi Lubos,

On 01/23/2011 08:17 AM, Lubos Kolouch wrote:
> Hello,
> 
> During doing backups I found strange behaviour... 2.6.37, latest btrfs-
> progs from git
> 
> nbgentoo ~ # btrfs subv crea a
> Create subvolume './a'
> nbgentoo ~ # cd a
> nbgentoo a # btrfs subv crea b
> Create subvolume './b'
> nbgentoo a # touch b/file
> nbgentoo a # ls -l b/
> total 0
> -rw-r--r-- 1 root root 0 Jan 23 08:14 file
> nbgentoo a # cd ..
> nbgentoo ~ # btrfs subv snap a x
> Create a snapshot of 'a' in './x'
> nbgentoo ~ # ls -l x/b/
> total 0
> 
> and also
> 
> nbgentoo ~ # cd x/
> nbgentoo x # btrfs subv dele b 
> ERROR: 'b' is not a subvolume
> 
> Is this a bug or intended behaviour and I am missing something something?
> How to snapshot a subvolume, containing another subvolumes?

It is the intended behavior. The snapshotting is not recursive about
subvolumes. If you snapshot a subvolume which contains another one, you
got only the content of the first subvolume.
The directory "x/b" which you see, is not the subvolume "b" snapshotted,
but only the "mount-point" of "b".


> 
> (I create subvolume backup, under this another subvolumes as not always I 
> want to snapshot the whole backup subvolume).
> 
> Thank you
> 
> Lubos
> 
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> 

Re: snapshot strange behaviour

[Lubos Kolouch]

Goffredo Baroncelli, Sun, 23 Jan 2011 13:17:13 +0100:

> Hi Lubos,
> 
> On 01/23/2011 08:17 AM, Lubos Kolouch wrote:
>> Hello,
>> 
>> During doing backups I found strange behaviour... 2.6.37, latest btrfs-
>> progs from git
>> 
>> nbgentoo ~ # btrfs subv crea a
>> Create subvolume './a'
>> nbgentoo ~ # cd a
>> nbgentoo a # btrfs subv crea b
>> Create subvolume './b'
>> nbgentoo a # touch b/file
>> nbgentoo a # ls -l b/
>> total 0
>> -rw-r--r-- 1 root root 0 Jan 23 08:14 file nbgentoo a # cd ..
>> nbgentoo ~ # btrfs subv snap a x
>> Create a snapshot of 'a' in './x'
>> nbgentoo ~ # ls -l x/b/
>> total 0
>> 
>> and also
>> 
>> nbgentoo ~ # cd x/
>> nbgentoo x # btrfs subv dele b
>> ERROR: 'b' is not a subvolume
>> 
>> Is this a bug or intended behaviour and I am missing something
>> something? How to snapshot a subvolume, containing another subvolumes?
> 
> It is the intended behavior. The snapshotting is not recursive about
> subvolumes. If you snapshot a subvolume which contains another one, you
> got only the content of the first subvolume. The directory "x/b" which
> you see, is not the subvolume "b" snapshotted, but only the
> "mount-point" of "b".
> 

Hi Goffredo,

I understand. But then I think btrfs should refuse to do it or at least 
print a warning. Otherwise it is very inconvenient for the user, having to
search for any subvolumes down the tree...

Lubos

Re: snapshot strange behaviour

[Goffredo Baroncelli]

On 01/23/2011 04:05 PM, Lubos Kolouch wrote:
> Goffredo Baroncelli, Sun, 23 Jan 2011 13:17:13 +0100:
> 
>> Hi Lubos,
>>
>> On 01/23/2011 08:17 AM, Lubos Kolouch wrote:
>>> Hello,

>>> Is this a bug or intended behaviour and I am missing something
>>> something? How to snapshot a subvolume, containing another subvolumes?
>>
>> It is the intended behavior. The snapshotting is not recursive about
>> subvolumes. If you snapshot a subvolume which contains another one, you
>> got only the content of the first subvolume. The directory "x/b" which
>> you see, is not the subvolume "b" snapshotted, but only the
>> "mount-point" of "b".
>>
> 
> Hi Goffredo,
> 
> I understand. But then I think btrfs should refuse to do it or at least 
> print a warning. Otherwise it is very inconvenient for the user, having to
> search for any subvolumes down the tree...


Sorry, but I can't agree. To me it seems a reasonable default. There are
a lot of cases where I would not snapshot a sub-sub-subvolume: my rootfs
is a subvolume, my home is in another one. I can snapshot, update the
root fs, then if something goes wrong I can roolback to the old one,
without affecting my home.

This behavior is strictly related to the btrfs internal.

Any way it is true that this behavior should be highlighted in the
documentation.

And more, it is possible to add a "-R" flag to snapshot recursively a
subvolume...

Goffredo

> Lubos
> 
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> .
> 

Re: snapshot strange behaviour

[Chester]

Also, btrfs already has a utility to scan for subvolumes in a directory

btrfs subvolume list /path

On Sun, Jan 23, 2011 at 12:02 PM, Goffredo Baroncelli
<kreijack@libero.it> wrote:
> On 01/23/2011 04:05 PM, Lubos Kolouch wrote:
>> Goffredo Baroncelli, Sun, 23 Jan 2011 13:17:13 +0100:
>>
>>> Hi Lubos,
>>>
>>> On 01/23/2011 08:17 AM, Lubos Kolouch wrote:
>>>> Hello,
>
>>>> Is this a bug or intended behaviour and I am missing something
>>>> something? How to snapshot a subvolume, containing another subvolu=
mes?
>>>
>>> It is the intended behavior. The snapshotting is not recursive abou=
t
>>> subvolumes. If you snapshot a subvolume which contains another one,=
 you
>>> got only the content of the first subvolume. The directory "x/b" wh=
ich
>>> you see, is not the subvolume "b" snapshotted, but only the
>>> "mount-point" of "b".
>>>
>>
>> Hi Goffredo,
>>
>> I understand. But then I think btrfs should refuse to do it or at le=
ast
>> print a warning. Otherwise it is very inconvenient for the user, hav=
ing to
>> search for any subvolumes down the tree...
>
>
> Sorry, but I can't agree. To me it seems a reasonable default. There =
are
> a lot of cases where I would not snapshot a sub-sub-subvolume: my roo=
tfs
> is a subvolume, my home is in another one. I can snapshot, update the
> root fs, then if something goes wrong I can roolback to the old one,
> without affecting my home.
>
> This behavior is strictly related to the btrfs internal.
>
> Any way it is true that this behavior should be highlighted in the
> documentation.
>
> And more, it is possible to add a "-R" flag to snapshot recursively a
> subvolume...
>
> Goffredo
>
>> Lubos
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrf=
s" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at =A0http://vger.kernel.org/majordomo-info.html
>> .
>>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-btrfs=
" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at =A0http://vger.kernel.org/majordomo-info.html
>
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" =
in
the body of a message to majordomo@vger.kernel.org
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Re: snapshot strange behaviour

[Lubos Kolouch]

Goffredo Baroncelli, Sun, 23 Jan 2011 19:02:11 +0100:

> On 01/23/2011 04:05 PM, Lubos Kolouch wrote:
>> Goffredo Baroncelli, Sun, 23 Jan 2011 13:17:13 +0100:
>> 
>>> Hi Lubos,
>>>
>>> On 01/23/2011 08:17 AM, Lubos Kolouch wrote:
>>>> Hello,
> 
>>>> Is this a bug or intended behaviour and I am missing something
>>>> something? How to snapshot a subvolume, containing another
>>>> subvolumes?
>>>
>>> It is the intended behavior. The snapshotting is not recursive about
>>> subvolumes. If you snapshot a subvolume which contains another one,
>>> you got only the content of the first subvolume. The directory "x/b"
>>> which you see, is not the subvolume "b" snapshotted, but only the
>>> "mount-point" of "b".
>>>
>>>
>> Hi Goffredo,
>> 
>> I understand. But then I think btrfs should refuse to do it or at least
>> print a warning. Otherwise it is very inconvenient for the user, having
>> to search for any subvolumes down the tree...
> 
> 
> Sorry, but I can't agree. To me it seems a reasonable default. There are
> a lot of cases where I would not snapshot a sub-sub-subvolume: my rootfs
> is a subvolume, my home is in another one. I can snapshot, update the
> root fs, then if something goes wrong I can roolback to the old one,
> without affecting my home.
> 
> This behavior is strictly related to the btrfs internal.
> 
> Any way it is true that this behavior should be highlighted in the
> documentation.
> 
> And more, it is possible to add a "-R" flag to snapshot recursively a
> subvolume...
> 
> Goffredo

The -R would be nice... two use cases :

1) directory many_small_files under the /home subvolume, that you need 
only for a while - it is easier to for example delete it when it is 
subvolume as well

2) backups

subvolume backups -> subvolumes 20110122, 20110123, ...
you want to delete backups older than x years -> it is much faster to do 
if it is a subvolume as well. But - you may as well want to be able 
snapshot or delete the whole backups subvolume.

Lubos

Re: snapshot strange behaviour

[Fajar A. Nugraha]

On Mon, Jan 24, 2011 at 1:02 AM, Goffredo Baroncelli <kreijack@libero.it> wrote:

> And more, it is possible to add a "-R" flag to snapshot recursively a
> subvolume...

Are you saying recursive snapshot creation is aready supportted in
btrfs? Which version?

-- 
Fajar