using a disk "mirrored" with dd

[Konrad Heuer]

On Tue, 3 Aug 2004, Matt wrote:

> I have a machine running 4.10-RELEASE-p2 with two identical hard disks
> -- ad0 and ad2. I would like to make a complete copy of the first disk
> to the second disk nightly for quick disaster recovery.
>
> I've dd'ed the disk as follows
>
> # dd if=/dev/ad0 of=/dev/ad2
>
> and edited the disklabel of the second disk to change ad0s1 to ad2s1 as follows
>
> # disklabel -e -r ad2
>
> However, I'm still unable to mount the root partion (or any other
> partition) of the second disk to tweak /etc/fstab etc. even though
>
> # mount /dev/ad2s1a /mnt
> mount: /dev/ad2s1a: Operation not permitted
>
> What am I missing? Is there anything else I need to do beyond editing
> the disklabel to allow me to use the "mirrored" disk?
>
> Output of disklabel for the two disks follows:
>
> # disklabel ad0
> # /dev/ad0c:
> type: ESDI
> disk: ad0s1
> label:
> flags:
> bytes/sector: 512
> sectors/track: 63
> tracks/cylinder: 255
> sectors/cylinder: 16065
> cylinders: 4864
> sectors/unit: 78156162
> rpm: 3600
> interleave: 1
> trackskew: 0
> cylinderskew: 0
> headswitch: 0           # milliseconds
> track-to-track seek: 0  # milliseconds
> drivedata: 0
>
> 8 partitions:
> #        size   offset    fstype   [fsize bsize bps/cpg]
>   a:   409600        0    4.2BSD     2048 16384    97   # (Cyl.    0 - 25*)
>   b:  5242880   409600      swap                        # (Cyl.   25*- 351*)
>   c: 78156162        0    unused        0     0         # (Cyl.    0 - 4864*)
>   e:  4194304  5652480    4.2BSD     2048 16384    89   # (Cyl.  351*- 612*)
>   f: 10485760  9846784    4.2BSD     2048 16384    89   # (Cyl.  612*- 1265*)
>   g: 18874368 20332544    4.2BSD     2048 16384    89   # (Cyl. 1265*- 2440*)
>
> # disklabel ad2
> # /dev/ad2c:
> type: ESDI
> disk: ad2s1
> label:
> flags:
> bytes/sector: 512
> sectors/track: 63
> tracks/cylinder: 255
> sectors/cylinder: 16065
> cylinders: 4864
> sectors/unit: 78156162
> rpm: 3600
> interleave: 1
> trackskew: 0
> cylinderskew: 0
> headswitch: 0           # milliseconds
> track-to-track seek: 0  # milliseconds
> drivedata: 0
>
> 8 partitions:
> #        size   offset    fstype   [fsize bsize bps/cpg]
>   a:   409600        0    4.2BSD     2048 16384    97   # (Cyl.    0 - 25*)
>   b:  5242880   409600      swap                        # (Cyl.   25*- 351*)
>   c: 78156162        0    unused        0     0         # (Cyl.    0 - 4864*)
>   e:  4194304  5652480    4.2BSD     2048 16384    89   # (Cyl.  351*- 612*)
>   f: 10485760  9846784    4.2BSD     2048 16384    89   # (Cyl.  612*- 1265*)
>   g: 18874368 20332544    4.2BSD     2048 16384    89   # (Cyl. 1265*- 2440*)
>
> Thanks for any insight, and let me know if you need to see anything else.

Did you do the dd-copy while the system was running multi-user from the
first disk? I'd expect larger problems then because the file systems
inconsistencies on the second disk may never be resolved.

If you did it in single user mode, a 'fsck -y' for each file system on the
second disk before trying to mount may help.

Best regards

Konrad Heuer
GWDG, Am Fassberg, 37077 Goettingen, Germany, kheuer2 at gwdg.de