20. Multiple Tape Backups

For the use of multiple tape backups, these are the following assumptions made.

20.1 Writing

End of tape is indicated by one of:

• error code == -1 && errno == ENOSPC
• zero bytes written
• less bytes written than we asked for

20.2 Reading

End of tape is indicated by one of:

• error code == -1 && errno == ENOSPC
• error code == -1 && errno == ENODATA
• returned less bytes than we asked for

End of volume is indicated by

• zero bytes read
• error code == -1 && errno == ENODATA

This is what ftape does for floppy controller tape drives. If are using another sort of tape drive, then the multiple tape backup feature will only work if the above is true. If it is not true and you are able to work out what your particular tape drive does, if you send me details, I will try and incorporate it into future releases. I'm especially interested in users of SCSI drives since I have no access to them.

If your tape drive doesn't support the above, you can use the --tape-size option to tell taper the size of your tape drive. Tape size is specified in megabytes, eg. --tape-size 120 means that your tape is 120MB, --tape-size 250 means that your tape is 250MB. Note that these must be uncompressed sizes. You must specify the same number every time you start taper - you can put it in your preference file if necessary. If you don't specify the same number, you will get very spurious, unpredictable results. Note that you should subtract about 10% from the manufacturers stated size to account for formatting etc.. (eg. for a 120MB tape, tell taper that it is 108MB).