> If I create a 3-disk RAID5 with those disks and then add a 4th > disk, after the reshape completes, I again have a component > size of 5237760, and overall array size of 16090398720, > matching that of the original 4-disk RAID5 But, now, if I try > and grow --size=max on that array, it *does* have an effect, > and the overall array size goes up by 4.5 MiB. "Growing" is a pretty hairy/desperate operation and should not be considered a normal case, but a last resort bad idea, so questions like this seem to me a bit otious... :-) > The overall array size went up by 4.5 MiB (because 3 * 1536 ?) My 2 pennies guess (and this question does not deserve more investigation) is that as a rule MD members have leading and trailing areas (for things like metadata blocks) and these vary quite a bit by kernel/'mdadm' version, so the already quite hairy "grow" code does some simplified rounding down. http://www.thomas-krenn.com/en/wiki/Linux_Software_RAID#Testing_the_Alignment
