How much room is left on my LTO3 tape?

For end of month, we do an additional SAVLIB *ALLUSR as well as a SAV of
important IFS directories to archive the month. To save some money, we
put multiple months on a single tape. We used to get 4 months on a
single tape, but recently the 4th month overflowed.

In Ye Days of Yore I could tell how full a tape was by looking at it. I
find that task a bit more difficult today. If I do a SAVLIB
OUTPUT(*OUTFILE) I get a 'saved size' in bytes but that doesn't help me,
given compaction. Also, the OUTFILE isn't available for the SAV command.

If I do a DSPTAP OUTPUT(*OUTFILE) I get a fun column named RDTRL1 that I
can parse out to find out how many blocks were used. That seems a more
reasonable way to figure out how big a given save set is but it also
seems somewhat painful.

Using the 'full' tape, I ran a query over the DSPTAP output and figured
out that 5,714,007 blocks are on that tape. So I at least have a first
approximation as to the capacity in blocks for my particular mix of data.

Is there a different way to work out in advance whether a given
partially full tape will hold another save set?

V5R4M5:

select substr(rdtrl1, 5, 15) as library, decimal(substr(rdtrl1, 54, 7),
7, 0) as blocks from ultlabels

select sum(decimal(substr(rdtrl1, 54, 7), 7, 0)) as blocktotal from u
ltlabels

--buck