Messages in this thread | | | From | "Yann E. MORIN" <> | Subject | Re: % more space reqd. when dd is used? | Date | Tue, 13 Nov 2001 10:54:25 +0100 |
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Vasu,
> hi all, > I have two physical harddisks /dev/hda1 and /hdb
You have two physical hard disks /dev/hda and /dev/hdb. - hda contains a partition /dev/hda1 you want to backup. - hdb contains at least one partition /dev/hdb1 on which you want to put the backup (unless you use the raw HD formatted).
I'll assume you'll backup to a file in /dev/hdb1.
> 1) i want to copy drive (take backup) to a file ( in /hdb)using dd. > So how much space( in terms percentage)more is required in /hdb > for it to be copied successfully.
Don't know the right answer. That shall not need too much overhead.
But I would point out that /dev/hda1 can _not_ be a live filesystem (I mean you can't do that if /dev/hda1 is mounted, for example as your root FS), if it is, you'll end up with a backup containing errors (due to cache).
$ umount /dev/hda1 $ mount /dev/hdb1 /hdb $ dd if=/dev/hda1 of=/hdb/backup
But if you want, you can also do this: $ umount /dev/hda1 /dev/hdb1 $ dd if=/dev/hda1 of=/dev/hdb1
That way, /dev/hdb1 needs to be exactly the size of /dev/hda1
> 2) After copying using dd if=/dev/hda1 of=/hdb/backup > how to retrive it back again in terms of directories and > sub-directories and files.
Two solutions here: - you want to restore /dev/hda1 at the state it was at backup, then you dd if=/hdb/backup of=/dev/hda1 (Note that once again /dev/hda1 must _not_ be mounted) - or you just want to access the backup. In this case you need a loop device: mount -o loop /hdb/backup /mnt/backup You'll need loop support in your kernel (either built-in or module). That way, you can compare the FS against the backup, and/or restore part of it (by cp'ing files/directories).
Correct me where I'm wrong.
Regards, Yann E. MORIN.
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