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Date:      Sun, 5 Aug 2012 23:12:48 -0700
From:      Matthew Navarre <navarre.matthew@gmail.com>
To:        freebsd-questions@freebsd.org
Subject:   Mounting raw disk backup file.
Message-ID:  <CAMZ_P7iuN0WXzvU3BZUovat8hvXYyjB68jz-GWnerkEgJOqrCg@mail.gmail.com>

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HI,
I had a drive fail recently, it was working fine until I rebooted. After
that the partition map was corrupt and I can't mount either partition on
the disk. So I made a copy of the whole disk using dd to an old USB drive.
There were several IO errors while dd was copying the disk, so I think the
disk is starting to go.

I can probably fix the partition table using testdisk, but now that I've
got this image file I'd rather work with that instead of the physical disk.
I've read the Handbook section on using mdconfig, but that assumes the
image file is of a filesystem, not a whole disk. I think I've
found instructions for how to do it on linux, but if there's a way to mount
it on FreeBSD I'd rather do that.

So, any suggestions?

Here's what file says about the file:
mnavarre@pcbsd-1810] /# file /mnt/ada1_backup
/mnt/ada1_backup: x86 boot sector; partition 1: ID=0xa5, active, starthead
1, startsector 63, 167766732 sectors; partition 2: ID=0xa5, starthead 254,
startsector 167766795, 144809910 sectors, code offset 0x3c, BSD disklabel

And just for grins, what fdisk says about the actual disk:
mnavarre@pcbsd-1810] /# fdisk ada1
******* Working on device /dev/ada1 *******
parameters extracted from in-core disklabel are:
cylinders=310098 heads=16 sectors/track=63 (1008 blks/cyl)

Figures below won't work with BIOS for partitions not in cyl 1
parameters to be used for BIOS calculations are:
cylinders=310098 heads=16 sectors/track=63 (1008 blks/cyl)

Media sector size is 512
Warning: BIOS sector numbering starts with sector 1
Information from DOS bootblock is:
The data for partition 1 is:
sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
    start 63, size 167766732 (81917 Meg), flag 80 (active)
        beg: cyl 0/ head 1/ sector 1;
        end: cyl 1023/ head 254/ sector 63
The data for partition 2 is:
sysid 165 (0xa5),(FreeBSD/NetBSD/386BSD)
    start 167766795, size 144809910 (70707 Meg), flag 80 (active)
        beg: cyl 1023/ head 255/ sector 63;
        end: cyl 1023/ head 254/ sector 63
The data for partition 3 is:
<UNUSED>
The data for partition 4 is:
<UNUSED>

Thanks,
Matt Navarre



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