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Re: Tool for semi-cloning a hard drive: recommendations?



Phil Meyer wrote:

No worries, I know about getting old. :)

Remember, dd originally meant 'disk duplicator'.

There has been much discussion here recently about what dd can and cannot do.

Maybe I can sum up. :)

1. Target drive cannot be smaller than the source drive, period.

2. inode and/or other fs related resources will be sized to the old drive.
This is only problematic when going to a much larger drive, or when the drive contains mostly small files.

I expect resize2fs and equivalents fix that.


3. udev/hal/+friends do not like foreign disk drives, and will duplicate some devices, causing new eth, sd and other devices. It is fine, and does mostly the right things, but may come as a surprise. Windows almost NEVER works from a cloned drive, sorry. For Windows, you really need a backup or 'ghost' type program.

I regularly copy Windows XP and Windows Server disks using Linux and changing size, sometimes smaller, sometimes larger; Knoppix is my preferred tool. I never have a problem, except when I do something stupid.



4. Moving a 'cloned' bootable drive to another host does not guarantee it will be bootable on the new host. A rescue on the new host may still be necessary to reinstall grub.

5. Trying to 'use' a cloned drive on the original host while the original drive is present is problematic due to the way Fedora mounts partitions by LABEL. Other Linuxen use the hard drive id (UUID, I think) just for this purpose.

I suspect that's imperfect too, but I've not put it to the test.


Those are the CAVEATS that come to mind, but with a bit of care, cloning with dd works just fine for ufs (Solaris) ext3/reiser, etc.

One last thing: its best to use a proper bs (block size) argument for dd so the sector boundaries will be honored. On drives with multiple fs types, you may need to punt back to the lowest common denominator which is likely 1k. Using block writes instead of single byte writes is also a bit faster.

dd always copies every last byte. Use of bs to copy larger chunks is good, it can speed the operation (particularly when source and target are the same drive).




--

Cheers
John

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