my GNU du doen't have a -d option either, but on Solaris -d means 'Do not cross filesystem boundaries.' the equivalent GNU option is -x or --one-file-system.

i've been toying with this backup thing for a couple of days, my new work provided home machine came with a DVD+RW drive that i want to put to some good use. but i have to admit i think it's much better/cheaper nowdays to get an extra HD for backups. mounting another 120G and using rsync beats the snot out of trying to fit things in 700M or 4.7G chunks.

but i've still been looking at the problem from the angle of 'it is easier to send my sister a DVD than a HD' and i'm working on a little script to do just that.

some tidbits from my digging...

• DVD it appears has a 2k block size. assuming some sort of regularish filesystem on the media it might be wise to support block size in the calculations. a 1b file will take at least 2k on the disk.
• i haven't found a way to calculate the iso9660 filesystem overhead except by running mkisofs with --print-size. if anybody knows the overhead calculations please share =).
• iso9660 has a max-filesize limit, it's either 1 or 2 G, i forget which. so you won't be able to back up that 3G file on a DVD the obvious way.
• mkisofs will automatically split those large files into filename_00, filename_01, filename_02, ... chunks. you'll have to put them back together yourself.
• if you have RW media and multisession capability there is a neato patch for mkisofs that will do incremental backups. something like:

  mkisofs -r -J -root=backup_00 /path
  plus
  mkisofs -r -J -root=backup_01 -old-root=backup_00 /path
  [download]

  if you burn the first iso, then the second as multisession when you mount the disk backup_01 will have the most recent files, plus hardlinks back to files that didn't change between backups. i haven't quite figured this out yet since DVD+RW multisession isn't working on Linux 2.6.0 yet (should be fixed soon).
• it might be more appropriate to use the -H option over -h. -h is 1024*1024 wise, -H is 1000*1000 wise. the 4.7G DVD is in -H units, not sure about 700M CD but i would guess it's in -H units also.

if anybody knows of any interesting and not too difficult algorithms for packing i would love to know about them. seems Algorithm::Bucketizer only has a couple that are either simple or random. i'd like to find something with a bit of heuristics added.