[Users] mount ploop image from read-only fs

[Roman Haefeli]

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
> 
> 
>