bandwidth and seek time of the disk, using the "4 * bandwidth * seek
time" formula from Neefe-Matthews' 1997 paper. An RZ25 disk with this
option gets 200K segments. Reference the paper in the manual page.
kernel.
Don't make more superblock segments than we have a record of in
the superblock; and print these out as we go, like newfs.
Add am "-M" flag to specify the number of reserved segments, with a note
in the man page not to use it.