RE: determine how full a tape is

[qsrvbas@xxxxxxxxxxxx]

midrange-l-request@xxxxxxxxxxxx wrote:

>   1. determine how full a tape is (Jim Franz)
>
>date: Fri, 11 Nov 2005 09:20:33 -0500
>
>Is there a command or any other way to determine how full (a percentage?)
>a cartridge tape is? Customer's backup is a single cartridge, and I am 
>preparing to add a large set of files. Need to see if nightly unattended backup
>will ask for 2nd tape. This is SLR60 tapes. Any formula w/block length and 
>file length from dsptap report?


I haven't looked into this for years. Back then, the unknown variable was the 
size and number of inter-record gaps -- the unused space between the end of one 
record/block on the tape and the start of the next. Gaps could simply be 
between blocks within a tape file or between file, possibly between the various 
file markers and the files, I'm not sure.

I'd swear that when I was looking into it, the storage density of tapes had 
reached the point where there was often more space in the gaps than in the 
actual data written to tape for many small files.

Because the ratio of gaps-to-data had gotten close to 1.0 in some cases, 
estimating how much "space" was left got to be tricky. You might store 1GB more 
on a tape if it was hundreds of small documents or 5GB if it was a single large 
file. (Exaggerating... maybe?)

In months/years after, tape technology got so complex, I didn't even try to 
search such things out anymore. Maybe somebody knows a site that has good 
_useful_ info.

Tom Liotta