[luau] use dd for disk clone?

[Ray Strode]

>
>
>dd seems to be file oriented, but I guess you   
>can just treat two mounted disks as files? 
>
It's not a good idea to do it on mounted disks (at lease read-write mounted
disks), but yes, you can just use the device names as if they were files.

>What would that look like, use /dev/hda and /dev/hdb as 
>
>stdin and stdout, something like that? 
>
Well, if you are trying to replicate one disk onto another, then that 
would work.
(Assuming the drives are identical. I'm not sure if it would work or not 
if, the
drives were different sizes/had different geometry).

so the command would be

dd if=/dev/hda of=/dev/hdb

or

cp /dev/hda /dev/hdb

If you want to make an image then you would do something like

dd if=/dev/hda of=mydrive.img

or

cp /dev/hda mydriveimage.img

If you just want to do one partition (say hda1), you would do:

dd if=/dev/hda1 of=mypartition.img

If you do your partitions separately, then it should be easier to
restore the data on a different size drive.

For instance,
dd if=mypartition.img of=/dev/hdb1

or

cp mypartition.img /dev/hdb1

One advantage of doing it by partition, is you should be able to 
actually mount
the image file as if it were a partition using the loopback filesystem.

mount myparition.img /mnt/mypartition -oloop

>If you use / it would cause a problem 
>because you'd be including your destination in your source, 
>right? 
>
I'm not sure i follow you here.  If you want to do a raw copy, then / 
isn't even
related, because / is a filesystem concept and raw copies don't know about
filesystems, they just know about bits.

>Isn't there also an issue regarding open files, etc.? When I  
>clone a disk in irix, the manual says to do it in single user 
>mode, I presume because you want all the files in a consistent 
>state.  
>
Yes.  Like i said, better to do it mounted as readonly, or not mounted 
at all.  Single
user mode would be a good way to ensure that.

>Anyone see a way of using dd to make a disk image file instead  
>of cloning a disk?  
>
See above.

>Would tar do? Tarball too big? Would tar be able to make an 
>exact copy? Would it leave out .files? 
>
Yes, tar would work I think, but would be a lot slower, because it would 
work at
the filesystem level instead of the bit level.   There are other issues 
to think about
two, like if you had more than one drive mounted, then tar would include 
the
contents of all mounted drives in the archive.

--Ray