[Users] mount ploop image from read-only fs

Pavel Odintsov pavel.odintsov at gmail.com
Mon Oct 27 05:41:28 PDT 2014 

Hello!

Devon need ability to mount ploop disks from read only storage.

On Sat, Oct 25, 2014 at 2:46 AM, Kir Kolyshkin <kir at openvz.org> wrote:
> Roman,
>
> Sorry for hijacking the thread, but back to the original problem.
> Can you tell why vzctl snapshot-mount (or ploop snapshot-mount)
> is/was not working for you? Ideally, please provide a detailed scenario.
>
> Kir.
>
>
>
> On 10/24/2014 05:25 AM, Roman Haefeli wrote:
>>
>> On Mon, 2014-09-15 at 14:49 +0400, Pavel Odintsov wrote:
>>>
>>> Hello!
>>>
>>> I found bug! Thx Maxim Patlasov for helping with ploop v1 BAT format.
>>>
>>> Please check version from git and it support ploop v1 and v2 correctly :)
>>
>> It seems, it's not yet working properly for me. I can mount the ploop
>> image, I can mount its filesystem, I can browse the folder structure and
>> everything seems fine, but when I try to read any text file from etc/ or
>> var/log/ I only see garbage or content that certainly belongs to a
>> different file. Something with alignment seems still not correct.
>>
>> Please tell me how I can give you more useful information.
>>
>> Roman
>>
>>
>>
>>>
>>> On Sun, Sep 14, 2014 at 2:15 AM, Pavel Odintsov
>>> <pavel.odintsov at gmail.com> wrote:
>>>>
>>>> Thank you for report, its very useful for investigation. But only one
>>>> difference between v1 and v2 is ploop disk size in header (32 vs 64
>>>> bit).
>>>> But I use 64 bit numbers anywhere and everything should work fine. But I
>>>> suppose alignment issues which not handled in my tool.
>>>>
>>>>
>>>> On Friday, September 12, 2014, Roman Haefeli <reduzent at gmail.com> wrote:
>>>>>
>>>>> On Fri, 2014-09-12 at 11:15 +0200, Roman Haefeli wrote:
>>>>>>
>>>>>> On Fri, 2014-09-12 at 10:56 +0200, Roman Haefeli wrote:
>>>>>>>
>>>>>>> Hi Pavel
>>>>>>>
>>>>>>> I might have some more information on the issue. It seems that only
>>>>>>> 'old' ploop images cannot be mounted by ploop_userspace. I actually
>>>>>>> don't quite know the ploop version I used for creating the 'old'
>>>>>>> ploop
>>>>>>> images,  but I know it works well with images created with ploop
>>>>>>> v1.6.
>>>>>>>
>>>>>>> Does ploop_userspace know about older image formats?
>>>>>>
>>>>>> No, it's also not the version.
>>>>>
>>>>> Yes, there are different versions... I must have checked on the wrong
>>>>> machine. ploop_userspace works well with images created by ploop v1.11,
>>>>> but not with images created by ploop v1.6.
>>>>>
>>>>> Sorry for the noise.
>>>>>
>>>>> Roman
>>>>>
>>>>>
>>>>>
>>>>>>> On Thu, 2014-08-28 at 22:53 +0400, Pavel Odintsov wrote:
>>>>>>>>
>>>>>>>> Hello!
>>>>>>>>
>>>>>>>> No, it's not depend on kernel version. I created issue for you and
>>>>>>>> will try to investigate:
>>>>>>>> https://github.com/FastVPSEestiOu/ploop_userspace/issues/10 please
>>>>>>>> track this github issue.
>>>>>>>>
>>>>>>>> On Thu, Aug 28, 2014 at 6:12 PM, Roman Haefeli <reduzent at gmail.com>
>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>> Some more info:
>>>>>>>>>
>>>>>>>>> It works on our test cluster where we have
>>>>>>>>> 2.6.32-openvz-042stab093.4-amd64 installed. The report from below
>>>>>>>>> is
>>>>>>>>> from a host node running 2.6.32-042stab081.3-amd64.
>>>>>>>>>
>>>>>>>>> Is ploop_userspace dependent on kernel version?
>>>>>>>>>
>>>>>>>>> Roman
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Thu, 2014-08-28 at 15:59 +0200, Roman Haefeli wrote:
>>>>>>>>>>
>>>>>>>>>> Hi Pavel
>>>>>>>>>>
>>>>>>>>>> Your tool comes in handy. That is exactly what we'd need.
>>>>>>>>>> However, I had
>>>>>>>>>> troubles using it. I did:
>>>>>>>>>>
>>>>>>>>>> $ ploop_userspace
>>>>>>>>>> /virtual/.snapshot/nightly.0/vz/private/2006/root.hdd/root.hdd
>>>>>>>>>>
>>>>>>>>>>    We process:
>>>>>>>>>> /virtual/.snapshot/nightly.0/vz/private/2006/root.hdd/root.hdd
>>>>>>>>>>    Ploop file size is: 4193255424
>>>>>>>>>>    version: 1 disk type: 2 heads count: 16 cylinder count: 81920
>>>>>>>>>> sector count: 2048 size in tracks: 20480 size in sectors: 41943040
>>>>>>>>>> disk in
>>>>>>>>>> use: 1953459801 first block offset: 2048 flags: 0
>>>>>>>>>>    For storing 21474836480 bytes on disk we need 20480 ploop
>>>>>>>>>> blocks
>>>>>>>>>>    We have 1 BAT blocks
>>>>>>>>>>    We have 262128 slots in 1 map
>>>>>>>>>>    Number of non zero blocks in map: 3998
>>>>>>>>>>    Please be careful because this disk used now! If you need
>>>>>>>>>> consistent backup please stop VE
>>>>>>>>>>    !!!ERROR!!! We can't found GPT table on this disk
>>>>>>>>>>    !!!ERROR!!! We can't find ext4 signature
>>>>>>>>>>    Set device /dev/nbd0 as read only
>>>>>>>>>>    Try to found partitions on ploop device
>>>>>>>>>>    First ploop partition was not detected properly, please call
>>>>>>>>>> partx/partprobe manually
>>>>>>>>>>    You could mount ploop filesystem with command: mount -r -o
>>>>>>>>>> noload /dev/nbd0p1 /mnt
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> Despite the errors, I tried to mount the ploop-partition:
>>>>>>>>>>
>>>>>>>>>> $ mount -r  -o noload /dev/nbd0p1 /mnt/
>>>>>>>>>>
>>>>>>>>>> and got:
>>>>>>>>>>
>>>>>>>>>>    mount: special device /dev/nbd0p1 does not exist
>>>>>>>>>>
>>>>>>>>>> Apparently, ploop_userspace wasn't able to read the GPT partition
>>>>>>>>>> table.
>>>>>>>>>>
>>>>>>>>>> Tell me, if you need further information.
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> Roman
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Tue, 2014-08-19 at 12:48 +0400, Pavel Odintsov wrote:
>>>>>>>>>>>
>>>>>>>>>>> Hello!
>>>>>>>>>>>
>>>>>>>>>>> You can mount ploop from RO root.hdd images with my tool:
>>>>>>>>>>> https://github.com/FastVPSEestiOu/ploop_userspace but it's not
>>>>>>>>>>> stable
>>>>>>>>>>> now. You can try it and provide feedback.
>>>>>>>>>>>
>>>>>>>>>>> On Tue, Aug 19, 2014 at 12:24 PM, Roman Haefeli
>>>>>>>>>>> <reduzent at gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> Hi all
>>>>>>>>>>>>
>>>>>>>>>>>> At the university I work, we plan to switch all containers
>>>>>>>>>>>> from simfs to
>>>>>>>>>>>> ploop images on the long run. Despite the many advantages of
>>>>>>>>>>>> using
>>>>>>>>>>>> ploop, there is one major drawback that keeps us from
>>>>>>>>>>>> switching
>>>>>>>>>>>> production already now: We can't mount ploop images from
>>>>>>>>>>>> read-only
>>>>>>>>>>>> snapshots. In case of a recovery of a single file, we have to
>>>>>>>>>>>> copy the
>>>>>>>>>>>> ploop image from the read-only snapshot to some read-write
>>>>>>>>>>>> storage in
>>>>>>>>>>>> order to be able to mount it and extract the file. For CTs
>>>>>>>>>>>> with huge
>>>>>>>>>>>> ploop-images this is a big hurdle.
>>>>>>>>>>>>
>>>>>>>>>>>> Wouldn't it be possible to add a some flag to the 'ploop'
>>>>>>>>>>>> utility to
>>>>>>>>>>>> allow mounting ploop images from read-only storage (by
>>>>>>>>>>>> bypassing some
>>>>>>>>>>>> checks or skipping to set the dirty flag or whatever is
>>>>>>>>>>>> necessary)?
>>>>>>>>>>>>
>>>>>>>>>>>> Cheers,
>>>>>>>>>>>> Roman
>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>> _______________________________________________
>>>>>>>>>>>> Users mailing list
>>>>>>>>>>>> Users at openvz.org
>>>>>>>>>>>> https://lists.openvz.org/mailman/listinfo/users
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
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>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
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>>>>
>>>>
>>>>
>>>> --
>>>> Sincerely yours, Pavel Odintsov
>>>
>>>
>>>
>>
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-- 
Sincerely yours, Pavel Odintsov

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