does ddrescue or dd has capability to update the content of an image file

jao_madn · April 15, 2011, 4:19pm

Hi

I would like to ask about the ddrescue or dd command imaging tool. is dd or ddrescue has a capability to update the created image so that i would not create a new image again if i want run the dd or ddrescue again. or if i will place it in the schedule task..

If not then is someone knows the same application that will provide the same task with additional capabilities to update an image.

Thanks for any reply.

DGPickett · April 15, 2011, 4:48pm

Suggest it as a enhancement. It might take longer than just creation, unless writing is exceptionally slow. It might be possible if they would lay down oldest files first, and if you restated them later, it would override. Then, it could overwrite from some point and for spot problems on old files, overlay their information at the end.

Corona688 · April 15, 2011, 5:06pm

If I get your meaning, dd doesn't magically know which blocks have changed so it can update only those blocks, no. You have to copy the whole disk again.

What more efficient tools are available for your needs depends on your system and your configuration.

jao_madn · April 15, 2011, 6:34pm

Thanks for the reply..

I just want to confirm ..and may i ask again if you know such package that works what i mention above.. Also i read somewhere. I can use rsync to backup my root partition and case problem can i restore it, the boot loader will be install via boot live CD grub-install command if restore and also restore in another partition. Is it possible that rsync way.

Corona688 · April 15, 2011, 7:07pm

That depends on your system and disk configuration. Checking the disk for changes or areas in use isn't easy if you want a disk image. What is it?

This doesn't have a lot to do with dd or dd_rescue. That takes a bare-metal backup, just clones disks sector-for-sector, rsync checks and updates individual files.

rsync checks individual files, so sounds more up your alley. A backup of files may take a lot more work to actually use than a bare-metal one though.

$ mkdir a b
$ touch a/stuff
$ rsync -r --delete a/ b
$ ls -l b/stuff
-rw-r--r-- 1 tyler users 0 Apr 15 17:07 b/stuff
$ rm a/stuff
$ rsync -r --delete a/ b
$ ls -l b/stuff
ls: cannot access b/stuff: No such file or directory
$

See man rsync for more options. If you're backing up your root partition you'll want -x so it doesn't leave the partition, and -a so it preserves users, groups, timestamps, etc, etc, etc. And -H so it preserves hardlinks.

jao_madn · April 16, 2011, 7:27am

corona688:

That depends on your system and disk configuration. Checking the disk for changes or areas in use isn't easy if you want a disk image. What is it? This doesn't have a lot to do with dd or dd_rescue. That takes a bare-metal backup, just clones disks sector-for-sector, rsync checks and updates individual files.

rsync checks individual files, so sounds more up your alley. A backup of files may take a lot more work to actually use than a bare-metal one though.
$ mkdir a b
$ touch a/stuff
$ rsync -r --delete a/ b
$ ls -l b/stuff
-rw-r--r-- 1 tyler users 0 Apr 15 17:07 b/stuff
$ rm a/stuff
$ rsync -r --delete a/ b
$ ls -l b/stuff
ls: cannot access b/stuff: No such file or directory
$
See man rsync for more options. If you're backing up your root partition you'll want -x so it doesn't leave the partition, and -a so it preserves users, groups, timestamps, etc, etc, etc. And -H so it preserves hardlinks.

Thanks corona688: I just want to know if it possible about what i mention in rsync root and install boot-grub via live cd. I know rsync and using it to backup my home partition.

Thanks by the way.