I agree, think of it as so many tapes.  Since they are 'really fast tapes',
being on disk, you might consider doing reclaimation at some unusually low
number to get expired data out of the way ASAP.  If you don't need the space
that badly, relax the reclaimation percentage a bit.  Instead of starting
withe 80 or 60 percent like you would on tapes, you might start with 40
percent and go to 20 percent if you need the space.

This still leaves you with about 20% of the library with 'old data', plus
your need for at least one or two 'scratch tapes' in the library at a
minimum!

If emulating LTO1 drives, at 100G each, 62T gives you about 600 (being
conservative) volumes.  Take away even 2 scratch volumes as a minimum for
scratch tapes and subtract 20% of the rest as 'expired data' you still get
(598 - 120) 478 volumes at 100G each of real data, or 47.8T on your 62T
library.

If you know your data, and know you get a real world 30% compression, then
it should find close to your 62T of data ( 47.8*1.3=62.14T but that is close
with this level of engineering estimate).  If you get better compression you
really win.

Depending on your needs, you could use client compression, or tape drive
compression.  There are religous camps on both sides, but I suggest you give
it a try both ways to see what you really get.

... green with envy ... JC