Hi, > Question: is this currently capable of updating a CD-R or DVD-R using > multi-session as the basis for updating selected files?
Yes. xorriso does multi-session on nearly any media (except the infamous fast-blanked DVD-RW). You may overwrite existing files in the ISO image, or delete them, or move them to another address path. If you add directories then they get merged with existing ones. So it might be desireable to delete the old one first. The according example from the man page: Manipulating an existing ISO image on the same media Load image from drive. Remove (i.e. hide) directory /sounds and its subordinates. Rename directory /pictures/confidential to /pictures/restricted. Change access permissions of directory /pictures/restricted. Add new directory trees /sounds and /movies. Burn to the same media and eject. $ xorriso -dev /dev/sr2 \ -rm_r /sounds -- \ -mv \ /pictures/confidential \ /pictures/restricted \ -- \ -chmod go-rwx /pictures/restricted -- \ -map /home/me/prepared_for_dvd/sounds_dummy /sounds \ -map /home/me/prepared_for_dvd/movies /movies \ -commit -eject all But if you want to mirror some hard disk subtrees by some trees on optical media, try this example: Incremental backup of a few directory trees This does the following to directories /open_source_project and /personal_mail in the ISO image: create them if not existing yet, compare them with their disk counterparts, add disk file objects which are missing yet, overwrite those which are different on disk, and delete those which have vanished on disk. But do not add or overwrite files matching *.o, *.swp. $ xorriso -dev /dev/sr0 \ -volid PROJECTS_MAIL_"$(date '+%Y_%m_%d_%H%M%S')" \ -not_leaf '*.o' -not_leaf '*.swp' \ -update_r /home/thomas/open_source_projects /open_source_projects \ -update_r /home/thomas/personal_mail /personal_mail \ -commit -toc -eject all To be used several times on the same media, whenever an update of the two disk trees to the media is desired. Begin with blank media and start a new blank media when the run fails due to lack of remaining space on the old one. This makes most sense with backups on non-erasable media like CD-R, DVD-R, DVD+R if the full backup leaves substantial remaining capacity on media and if the expected changes are much smaller than the full backup. An update run will probably save no time but last longer than a full backup. Other good reasons may be given if read speed is much higher than write speed or if file size changes happen too often within the write time of a full backup. With mount option "sbsector=" it is possible to access the session trees which represent the older backup versions. With CD media, Linux mount accepts session numbers directly by its option "session=". Multi-session media and most overwriteable media written by xorriso can tell the sbsector of a session by xorriso option -toc. Sessions on multi-session media are separated by several MB of unused blocks. So with small sessions the payload capacity can become substantially lower than the overall media capacity. If the remaining space on media does not suffice for the next gap, the drive is supposed to close the media automatically. Better do not use your youngest backup for -update_r. Have at least two media which you use alternatingly. So only older backups get endangered by the new write operation, while the newest backup is stored safely on a different media. Always have a blank media ready to perform a full backup in case the update attempt fails due to insufficient remaining capacity. > Clearly I could write whole new media, that's not optimal from a time or > storage space perspective, writing a new DVD for a 3-4kB file change is > undesirable. The waste of space on multi-session media is worst on CD-R[W] and DVD-R[W] where session gaps can be up to 20 MB. On DVD+R it is only 4 MB. Best it is with overwriteables: DVD-RAM, DVD+RW, formatted DVD-RW. There the waste is between 0 and 62 KiB. Another overhead is caused by the fact that with each session a complete new directory structure is written. The size depends on the number of file objects in the image and usually is in the range of a single percent of the combined image size. So the wish to write in granularity of few KiB will hardly be fulfillable by xorriso. My backups produce one base session of 200 MB and 20 small update sessions on CD media, one base session of 800 MB and 40 update sessions on DVD-R, 50 on DVD+R and 60 on DVD+RW. About 4500 blocks of each session hold the directory tree. (One can measure by making two runs with only a small data file changed inbetween.) Exanmple of a DVD-R: TOC layout : Idx , sbsector , Size , Volume Id ISO session : 1 , 0 , 870113s , UPDATE_HOME_2008_04_18_220030 ISO session : 2 , 908176 , 22632s , UPDATE_HOME_2008_04_20_133303 ISO session : 3 , 938656 , 19169s , UPDATE_HOME_2008_04_21_153459 ... ISO session : 41 , 2233968 , 60302s , UPDATE_HOME_2008_06_06_114440 DVD+-R multi-session info might be ignored or misunderstood by DVD-ROM drives. In that case one has to help mount to find the youngest session. This problem does not apply to overwriteable media. Have a nice day :) Thomas -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]