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8.2.2: File mark implementation with zftape

A major change in zftape compared with the former ftape-2.x and the sftape driver from pre-3.04 ftape distributions is the use of a volume-table segment as specified in the QIC-80/3010/3020 and QIC-113 development standards (http://www.qic.org). The driver doesn't use the failed sector log any more for file mark emulation but produces a volume table entry for each file written to tape.

The drawback of this approach is that there is a limit on the maximum number of file marks available per cartridge. Each file marks consumes 128 bytes in the volume table segment, the volume table segment has a size of 29k which yields a maximum number of 232 file marks. The volume table overflow extension as proposed by various qic standards (see http://www.qic.org) is not supported by ftape.

The portions of the tape that are occupied by data written with zftape can be recognized by other programs that implement that QIC standards (think for example of the software that was shipped with your tape drive). One can test this by doing a backup with zftape (using the `/dev/qft*' or `/dev/zqft*' devices, see zftape devices) and then use the software that came with your tape drive (you probably have to reboot to do this) and try to have a look at the volume table of the tape. There should be entries containing volume labels like

zftape volume 004

However, you will recognize that the time stamp that will be shown by such a program either makes no sense at all or is really out of date.

Note: it is still possible to read tapes that were written with the original ftape-2.x driver and the sftape driver from pre-3.04 ftape distributions (zftape does accomplish this by emulating a volume table). But write access to the tape is denied until you erase it which damages the data on the tape, of course. See zftape devices compatibility.


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