Archive Tapes

[Bob Turner]

In article <1990May2.113532.26951 at msuinfo.cl.msu.edu> jhl at frith.uucp (John Lawitzke) writes:
>From article <29490 at cup.portal.com>, by Dante_A_Nicolello at cup.portal.com:
>> Problem two:
>>         When the tape reaches the end of the cartridge, not the end of the
>> current track, unix produces a "write() error" instead of prompting
>> me to switch tapes.
>
>tar and cpio have no idea how long or how dense your tape is. They
>assume you will not attempt to write more to tape than it can hold. If
>you use the backup program you can specifiy density and length so the
>program knows when it needs to prompt for a new tape.
>
>One solution is find the source to pdtar and hack it to prompt for a new
>tape at the necessary point.
>
On a consulting job I did in March we had the same problem. Especially with
cpio. We were using a 499 and a 60MB Fastape.

Tar is an easy. It does not recognize the end of tape in any situation. But
all is not lost. It keeps count of the number blocks written so far. And 
compares it the number of blocks available that was specified on the
command line or in the file /etc/defaults/tar (or something like that). 
If you want specifics I will be happy to post.

Cpio is a different beast.

Cpio according to the manual :-), is supposed to detect the end of 
the device and prompt for a new filename. Usually you key in the tape
again after you change the cartridge. Unfortunately, it actually works as
you describe. The problem seems to lie within the device driver that 
Archive supplys. The device driver when it hits the end of the tape returns 
a write error #5 (or something approximating it) which is the general I/O 
Error rather than no more space on device (Error number 27).
So that cpio knows to prompt. The unfortunate part is that the backup 
script also uses cpio. Realize that there is obvoiusly no problems unless
you need to span a tape.

If you need more help, mail me a message.

						Bob
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Bob Turner                    Network Manager, School of Engineering
513-229-3171                           turner at udecc.engr.udayton.edu
Univ. of Dayton, Engineering Computing Center-KL211, Dayton OH 45469