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NeddySeagoon
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Joined: 05 Jul 2003
Posts: 54577
Location: 56N 3W
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 Posted: Sat Apr 24, 2021 7:27 pm Post subject: Mount a Filesystem from a Sparse Disk Image [Understood] |
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Team,
I have a sparse *vhd file that looks like a HDD but isn't quite.
There is a header for Virtualbx at the start and the real disk image starts at 0xa800.
| Code: | | losetup -fP -o 0xa800 /home/roy/VirtualBox\ VMs/Gentoo_09-April-2003_i586_root.vhd |
does its thing and gets me /dev/loop0 and its two partitions.
| Code: | | fdisk -l /dev/loop0 |
shows me the partition table correctly.
Trying | Code: | | mount -o ro /dev/loop0p2 /mnt/floppy |
fails and dmesg tells me
| Code: | [21445.925728] loop0: p1 p2
[21445.925762] loop0: p2 size 41849325 extends beyond EOD, truncated
[21575.692938] EXT4-fs (loop0p2): VFS: Can't find ext4 filesystem |
Decoding the partition table and adding the offset says that
| Code: | # mount -t ext3 -o ro,offset=0x2743200 /home/roy/VirtualBox\ VMs/Gentoo_09-April-2003_i586_root.vhd /mnt/floppy
mount: /mnt/floppy: wrong fs type, bad option, bad superblock on /dev/loop0, missing codepage or helper program, or other error. |
is the same thing.
Its a disk image in a sparse file. Its not supposed to be all there. What have I missed?
_________________
Regards,
NeddySeagoon
Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.
Last edited by NeddySeagoon on Sun Apr 25, 2021 10:51 am; edited 1 time in total |
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molletts
Tux's lil' helper
Joined: 16 Feb 2013
Posts: 129
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| Posted: Sun Apr 25, 2021 10:19 am Post subject: |
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Is it an actual proper sparse file or does VirtualBox use some kind of proprietary format for its dynamic disk images?
If it's truly a sparse file, its size as reported by 'ls -l' will be the reported size of the disk plus any headers, not the size of the contained data.
For example, I just created a 1TB sparse file on a 120-odd GB partition:
| Code: | $ ls -l /media/alpha/big-sparse-file
-rw-r--r-- 1 stephen users 1099511627776 Apr 25 10:05 /media/alpha/big-sparse-file
$ df /media/alpha
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sda4 129232268 63626372 58998220 52% /media/alpha |
If I set up a loop device and create a partition table on it, fdisk reports the full available size despite the disk it's actually on being far smaller:
| Code: | # fdisk -l /dev/loop1
Disk /dev/loop1: 1 TiB, 1099511627776 bytes, 2147483648 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
Disklabel type: dos
Disk identifier: 0x2ee1f4bb
Device Boot Start End Sectors Size Id Type
/dev/loop1p1 2048 2147483647 2147481600 1024G 83 Linux |
If it's a proprietary format, the easiest solution might be to attach it to a VM (even a temporary one running the minimal install image or something) and copy the data out to a real sparse file using 'dd conv=sparse'.
Hope this is some help!
Stephen |
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NeddySeagoon
Administrator
Joined: 05 Jul 2003
Posts: 54577
Location: 56N 3W
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| Posted: Sun Apr 25, 2021 10:51 am Post subject: |
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molletts,
Thank you for that insight.
| Code: | $ ls -l /home/roy/VirtualBox\ VMs/Gentoo_09-April-2003_i586_root.vhd -h
-rw------- 1 roy roy 2.6G Apr 20 13:51 '/home/roy/VirtualBox VMs/Gentoo_09-April-2003_i586_root.vhd' |
Its not a real sparse file, That should be about 20G.
I'll fix VirtualBox and do it properly. Copying things out is not trivial. That VB really is a 09-April-2003_i586_root so ssh, and friends no longer work.
Telnet is still good though and nfs ver3 work.
_________________
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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