> > 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. Do you know if the refusal would include an error message clearly indicating why the growth is 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. I'm no longer using LVM on any of the servers, and I've converted to XFS on RAID 5 and RAID 6 arrays. At this time XFS does not support shrinking. I've seen some chatter on the web about 3rd party utilities which might make it possible. For growing an array, this would be a bit of a pain, but probably not a show stopper. Even for a failed drive I could probably just send the new drive back and purchase a different model whose real size is as large or larger than the extant drives. The problem is, waiting that long for a new drive or doing anything significant (like multiple shrinks!) to a partially failed array sends shivers up my spine. I may have to rethink my position on using raw drives. If I partition the drives, I can make the partition a bit smaller than the whole drive, allowing for the addition of a future drive whose size is a bit off. I hate to waste space, but being stuck with an undersized or limping array is worse. -- 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
