NeilBrown wrote: > On Mon, Oct 09 2017, Wakko Warner wrote: > > > Phil Turmel wrote: > >> A certain amount of the trouble with all of this is the english meaning > >> of "grow" doesn't really match what mdadm allows. > >> > >> Might it be reasonable to reject "--grow" operations that reduce the > >> final array size, and introduce the complementary "--reduce" operation > >> that rejects array size increases? > >> > >> Both operations would share the current code, just apply a different > >> sanity check before proceeding. > >> > >> mdadm would then at least not violate the rule of least surprise. > > > > As a general user of md raid and as a reader of the list, I would agree that > > this would be a better solution. Thinking in terms of lvm, there's lvreduce > > and lvextend. IMO, --force wouldn't be needed for --reduce (I was orginally > > thinking of --shrink) > > > > On a side note, is it possible for the lower layers to know what the last > > used sector is? IE lvm ontop of raid and has 10% allocated and the last > > sector is around the 10% mark. (If this were possible --force would be, > > required if shrinking would result in inaccessible data) > > No it isn't. I've occasionally thought of adding functionality so that > the a device could ask its client (e.g. filesystem, lvm, etc) if > shrinking is OK - but it hasn't happened yet. That's what I thought but wasn't sure. Thanks. > > I recently did a shrink of 4x 2tb drives so that I could replace the 2tb > > drives with 80gb drives (yes, big shrink!) Would have been nice for mdadm > > to know the smallest size was that wouldn't destroy my lvm volumes that were > > on top. > > Guess, try, see if data is still accessible. If not, revert the change. > If you have a filesystem on the raid, fsck will complain if you made it > too small. I don't know what you would try with lvm. pvscan? Fortunately for me, my first try worked. -- Microsoft has beaten Volkswagen's world record. Volkswagen only created 22 million bugs. -- 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
