RAID1 arrays don't have a chunk size, but if you ever convert
one to RAID5 you will need at least a small one >= 4K.
So round of size to a multiple of 64K.
This only affect Create, not "--grow --size=max". The latter
is too hard and with smaller returns.
Signed-off-by: NeilBrown <neilb@suse.de>
A small bitmap-chunksize hurts performance without helping
resync speed much - particularly on internal bitmaps.
So set the default to at least 64Meg.
Signed-off-by: NeilBrown <neilb@suse.de>
NeilBrown