Hi, Tim Woodall wrote: > cdromSHA=$( dd status=progress if=/dev/cdrom bs=1k count=$maxsize | > sha1sum | cut -d' ' -f1 ) > [...] > It's unusual, but I have had instances where the burn has completed > without any issues but the verify has failed. When that happens I got > several failures close together - I've assumed faulty disks.
Verification errors without i/o error from the block layer (forwarded by dd) are indeed very unusual. Normally the checksums in the data sectors of optical media let the drive detect bad readability and cause it to report an error to the operating system. I can only remember one occasion when a DVD was readable but with wrong checksum by one drive. Three others reported i/o error. One other was able to produce the correct checksum. I am paranoid enough to equip everything in my backups with MD5 checksums, and to checkread important old backups from time to time. I make daily incremental backups of $HOME on 1 BD-R, 3 BD-RE, and 1 DVD+RW. The DVD+RW gets zisofs compression, because else it would be too small even for the ~ 4.5 GiB base backup. Every other day i make incremental backups by scdbackup of my larger multi-media data and $WORK data. Either on a single BD-RE or on 1 to 4 DVD+RW. When the changed data exceed that size, i put the old backup level on shelf and start a new one with the old as base. > I have > never had an issue accessing old backups (which I do from time to time) Nevertheless consider to add a file with a list of checksums for the data files on the medium. This way you can later distinguish bad files from good ones, if the overall media verification fails. Have a nice day :) Thomas
