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snarksdad
n00b
Joined: 23 Sep 2016
Posts: 19
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 Posted: Tue Oct 18, 2016 5:05 pm Post subject: mounting raid partition from disk image file. |
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Fellow Gentooers..
This must be something simple I am just missing.
I have a disk image file I created with dd.
It looks like this:
fdisk -l fred.image.dd
Disk fred.image.dd: 4131 MB, 4131864576 bytes
255 heads, 63 sectors/track, 502 cylinders, total 8070048 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00033357
Device Boot Start End Blocks Id System
fred.image.dd1 2048 18431 8192 83 Linux
fred.image.dd2 22528 862207 419840 fd Linux raid autodetect
fred.image.dd3 866304 931839 32768 fd Linux raid autodetect
So I want to mount partition 2, I tried:
mount -o loop,offset=22528 fred.image.dd /mnt/loop
Which results with "mount: you must specify the filesystem type"
When I mount the physical device:
mount /dev/sdd2 /mnt/mydisk
I would get:
mount: unknown filesystem type 'linux_raid_member'
So there I use mdadm to "Assemble" a drive that I can mount:
mdadm -A -R /dev/md9 /dev/sdd2
mdadm: /dev/md9 has been started with 1 drive.
and then:
mount /dev/md9 /mnt/mydrive
Which succeeds and all is good.
So is there an analogous command option from mdadm that "emulates" the offset/assemble when using an image file
or is there some better way to mount this partition from the image file...
Thanks,
Snarksdad |
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NeddySeagoon
Administrator
Joined: 05 Jul 2003
Posts: 54244
Location: 56N 3W
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| Posted: Tue Oct 18, 2016 5:30 pm Post subject: |
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snarksdad,
The piece of the puzzle you are missing is the raid metadata version.
For metadata version 0.90, the raid metadata is at the end of the volume, so what you are trying to do works.
For metadata version 1.2, the raid metadata is at the start of the partition, where your mount expects the filesystem to start, so this fails.
No matter, on Linux, everything is a file, so
| Code: | | mdadm -A -R /dev/mdX /path/to/fred.image.dd2 |
should start mdX just as with the physical drive.
You can then mount mdX in the normal way.
The alternative is to look up the size of of the raid superblock, then use the offset= option to mount, so mount finds the actual start of the filesystem.
This is left as an exercise for the reader
For a read only mount, it doesn't matter much. For a rw mount the first option is preferred as it updates the raid metadata too.
| Code: | $ sudo mdadm -E /dev/sda5
Password:
/dev/sda5:
Magic : a92b4efc
Version : 0.90.00
... |
That should work on your image too.
_________________
Regards,
NeddySeagoon
Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail. |
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snarksdad
n00b
Joined: 23 Sep 2016
Posts: 19
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| Posted: Tue Oct 18, 2016 6:26 pm Post subject: |
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| NeddySeagoon wrote: | snarksdad,
The piece of the puzzle you are missing is the raid metadata version.
For metadata version 0.90, the raid metadata is at the end of the volume, so what you are trying to do works.
For metadata version 1.2, the raid metadata is at the start of the partition, where your mount expects the filesystem to start, so this fails.
No matter, on Linux, everything is a file, so
| Code: | | mdadm -A -R /dev/mdX /path/to/fred.image.dd2 |
should start mdX just as with the physical drive.
You can then mount mdX in the normal way. |
Hmm. Well I guess I had already tried this:
mdadm -A -R /dev/md9 /root/fred.image.dd2
mdadm: cannot open device /root/fred.image.dd2: No such file or directory
mdadm: /root/fred.image.dd2 has no superblock - assembly aborted
Which I figured meant mdadm is not actually not opening the image file (fred.image.dd)...
So I tried it on the image file itself (hoping mdadm would provide useful feedback):
mdadm -A -R /dev/md9 /root/fred.image.dd
mdadm: /root/fred.image.dd is not a block device.
mdadm: /root/fred.image.dd has no superblock - assembly aborted
Thanks,
Snarksdad |
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frostschutz
Advocate
Joined: 22 Feb 2005
Posts: 2977
Location: Germany
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| Posted: Tue Oct 18, 2016 6:34 pm Post subject: |
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| if you have partitions in a file, use `losetup --find --show --partscan file` and you'll get it via /dev/loopXpY which you can then assemble into a RAID and mount. |
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snarksdad
n00b
Joined: 23 Sep 2016
Posts: 19
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| Posted: Tue Oct 18, 2016 7:04 pm Post subject: |
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| frostschutz wrote: | | if you have partitions in a file, use `losetup --find --show --partscan file` and you'll get it via /dev/loopXpY which you can then assemble into a RAID and mount. |
Not familiar with this command, output not real helpful...
losetup --find --show --partscan fred.image.dd
/dev/loop1
# mount /dev/loop1 /mnt/test
mount: you must specify the filesystem type
root@localhost ~ #
root@localhost ~ # mount -o loop /dev/loop1 /mnt/loop
mount: you must specify the filesystem type
root@localhost ~ #
root@localhost ~ # mdadm -A -R /dev/md9 /dev/loop1
mdadm: Cannot assemble mbr metadata on /dev/loop1
mdadm: /dev/loop1 has no superblock - assembly aborted
What does one do with /dev/loop1?
Thanks,
Snarksdad |
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frostschutz
Advocate
Joined: 22 Feb 2005
Posts: 2977
Location: Germany
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| Posted: Tue Oct 18, 2016 7:45 pm Post subject: |
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there should be partitions ( /dev/loopXpY )
cat /proc/partitions
ls -l /dev/loop* |
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snarksdad
n00b
Joined: 23 Sep 2016
Posts: 19
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| Posted: Wed Oct 19, 2016 3:43 pm Post subject: |
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| frostschutz wrote: | there should be partitions ( /dev/loopXpY )
cat /proc/partitions
ls -l /dev/loop* |
Oh. I get it....
mdadm -A -R /dev/md9 /dev/loop1p2
mdadm: /dev/md9 has been started with 1 drive.
mount /dev/md9 /mnt/loop
mount: warning: /mnt/loop seems to be mounted read-only.
That does seem to work....
Thanks!
Snarksdad |
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