I've taken the patch supplied in the PR, but added a cross-reference to zip(1) to make files to span floppies etc (if anyone still fancies doing that).
-B option of pax says that it limits the number of bytes
written to a volume, but when the -z option is also used
the number of bytes written is less than that specified,
by the compression ratio. For example, see
How-To-Repeat.
Fix:
Add a sentence or two to the description of the -B option
along the lines of:
"Note that the specified size is for the pax image
itself. If the -z option is also used, the resulting
file may contain fewer bytes, according to the
compressibility of the archive contents."
Alternatively, perhaps the pax author could be persuaded
to run the archive size counter on the _output_ of the
gzip pipe? That would certainly be more useful.
How-To-Repeat: You won't get the same result, because you don't have my
file system contents, but any file tree should do (other
than one full of MP3 files or the like...)
pax -w -t -z -f /backup/full-${today_d}.pax -B667m $dirs
resulted in the warning message
"pax: User specified archive volume byte limit reached."
but a subsequent listing of the /backup directory shows:
-rw-r--r-- 1 root wheel 352215042 Jul 29 03:11 full-020729.pax