On 28/06/2009 19:31, Leslie Rhorer wrote:
I have a few questions. Some RAID implementations will simply refuse to create or grow an array if all the targets are not precisely the same size. Clearly this is not the case for mdadm. Not all drives of a given "size" are actually precisely the same size, however, and I am using unpartitioned drives for my RAID systems. What happens if I add a drive whose apparent physical size is a bit smaller than the device size used to create the array?
For RAID 4/5/6, I think it'll be refused. You have to shrink the filesystem, and LVM if you use it, then the array, so the used size is no bigger than the new drive - as you've noted, md doesn't mind if it doesn't use all the available space on its constituent devices. If it's a small reduction, as I imagine it would be, and your filesystem supports shrinking, it won't take long to do the the shrinks. Then adding the new drive will be painless. If your filesystem won't shrink - and some (many?) won't - I suspect you're scuppered.
It has to be that way because md can't (currently?) tell whatever's layered over it to change itself (though I think (guess) that to some extent this may change at some point in the future with some of the topology stuff that's been discussed here recently).
I don't know what RAID 0/1/10 would do but I imagine they'd be the same. Cheers, John. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
