on a disk with non zero stripesize (e.g. disks with 4k sector size)[1].
Also do not use automatic alignment when size is exactly specified, but
an alignment is not. Use automatic alignment only for case when user
omits both "-s" and "-a" options.
Reported by: Mikael Fridh <frimik at gmail> [1]
Approved by: re (kib)
MFC after: 1 week
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