LVM miscalculates bitmap size with small extent, so start with 16K as
for other RAID types.
Until version 2.02.103 LVM counts metadata segments twice when checking
available space, reduce segment count by one to account for this bug.
Write activity with LVM/RAID can happen after filesystem is unmounted.
In my testing modification time of loop files was 15 - 20 seconds
after unmount. So use time as close to unmount as possible as
reference instead.
