Re: Some help with dd backing up into an iso

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

the restore scenario for the xorriso backup would be like this:


- Prepare the storage device to which you want to restore.
  This may be as simple as choosing some directory in a filesystem with
  enough free space, or as complicated as setting up a new operating
  system on a freshly purchased hard disk.


- If the backup has some history of copying or transmission (e.g. by
  being burned to a DVD), then first let xorriso check whether it is
  still undamaged:

    iso=/dev/sr0

    xorriso -for_backup -indev "$iso" -check_media --

  will check the MD5 of superblock and directory tree and then read the
  whole ISO sequentially to look for the MD5 checksum tags. Those MD5s
  were stored by xorriso during the write run with setting -for_backup.

  Example of how a goot verification should look like (with lower speed
  if read from a real DVD):

    xorriso : UPDATE : Found matching MD5 superblock tag: start=32 size=18
    xorriso : UPDATE : Found matching MD5 tree tag: start=32 size=302
    xorriso : UPDATE : Found matching MD5 session tag: start=32 size=81217
    xorriso : UPDATE : 81250 blocks read in 1 seconds = 120.1xD
    Media checks :        lba ,       size , quality
    Media region :          0 ,      81250 , + good
    Media region :      81250 ,        158 , 0 untested
    MD5 checks   :        lba ,       size , result
    MD5 tag range:         32 ,      81217 , + md5_match

  "Media region" with quality "+ good" means that there were no i/o errors.
  "0 untested" means that these blocks are not claimed by the ISO filesystem.

  "MD5 tag range" with result "+ md5_match" means that the MD5 checksum
  of the inspected region matches the recorded MD5.


- If you just want to pick some files by help of your favorite file
  copier tool, then mount the medium

    iso=/dev/sr0
    sudo mount "$iso" /media/user/iso

  or if the ISO is in a data file rather than on a DVD

    iso=usb_part1.iso
    sudo mount -o loop "$iso" /media/user/iso

  Now you may copy files from /media/user/iso to the place where you want
  them to be. My favorite would be cp with option -a, possibly under sudo
  control for the power to assign file ownerships.
  (Caution: This can of course shoot your foot if you do not take care
            when composing the cp command.)


- If you want to copy the whole ISO content from DVD to a directory tree
  on hard disk or if ACLs and Extended Attributes matter, it is advisable
  to let xorriso copy the files out of the ISO:

    target=/my/prepared/restore/directory

    sudo xorriso \
     -osirrox on:sort_lba_on:auto_chmod_on \
     -for_backup \
     -indev "$iso" \
     -extract / "$target"

  Only the superuser or sudo are permitted to assign file ownership to
  other users. Omit "sudo" if all restored files shall belong the user
  who operates xorriso.

  The -osirrox setting "on" enables command -extract. Setting "sort_lba"
  lets xorriso read the files from DVD in the order of their content
  block addresses. This avoids slow and loud laser head movements.
  Because this reading order may cause revisiting of directories which
  were already restored without wx-permission, the setting "auto_chmod_on"
  permits xorriso to temprorarily grant its user those permissions.


Have a nice day :)

Thomas