Linda - Yup, I understand that the top level vdevs can't be removed from a pool. In fact, farther down in the original note, I'd written "I think that it is true that one cannot remove a vdev from a ZFS pool. " That is, however, not what I'm trying to do. If anyone is willing to read beyond the first sentence of the original message, I'm interested in your input. :-) Thanks Thomas On Mar 21, 2015 10:03 AM, "Linda Kateley" <lkateley at kateley.com> wrote: > The answer is no. Top level vdev can't be removed from a pool. Raidsets > can't be changed in number of disks used. You can replace disks with bigger > or smaller disks. > > If you want more help feel free to contact me directly I teach zfs classes > for a living :) > > Sent from my iPhone > > On Mar 20, 2015, at 9:12 PM, T L <tlunde at gmail.com> wrote: > > Does anyone know if I can "stack" and (later) "unstack" vdevs from a ZFS > pool? > > (Apropos my last message, this question would be germane to ZFS on Linux > as well as on BSD, FreeNAS, et al. ) > > I think that it is true that one cannot remove a vdev from a ZFS pool. (If > that's wrong, please correct me and the rest is irrelevant. ) > > Any pool (similar to LVM on Linux) that is larger than the space of a > single drive must contain multiple vdevs. For redundancy, a vdev is often ( > but not necessarily) more than a single drive; a vdev can be two or three > mirrored drives or 3+ drives in RAIDZn. > > So, if one has a RAIDZ1 set of 2T drives, one would have 4T of usable > space. To go to 6T of usable space, one would fail and replace each 2T > drive with a 3T drive. When the last drive is replaced, the space would > expand to 6T. > > My concern is the limited drives that can fit in a case. Say that I can > have up to 8 drives. I could use 4 pairs of 2T drives, each pair being a > vdev. When I start upgrading to 3 or 4T drives, I've still got to have 4 > vdevs in my pool. > > Would it be possible to have the drives set so that I have each pair of > drives (striped) make up a vdev and then create a vdev made up of a > mirrored pair of those striped pairs and then make the pool up of that > mirrored pair of vdevs? (In this way, there would only be 2 vdevs at the > pool level, rather than 4. ) > > The point is that, when I go from 2T drives to 4T drives, I can replace a > striped pair of 2Ts with a single 4T drive (i.e. a vdev with a single > member). Thus, after replacing all 2s with 4s, lets my pool will still have > a pair of (mirrored) vdevs. And that, in turn, then lets me add additional > drives to the box (and space to the pool) by adding 4 more drives (each > being a part of a mirrored pair, making up 2 more vdevs which get added to > the original 2 vdevs in the pool). > But the cool thing is that I'd get the benefit of the upgrade without > having to replace every drive; I'd see more space in the pool as soon as I > start adding the third vdev (either as the 9th and 10th devices, or after > replacing 4 of the 2s with (4) 4T drives). > > What happens when I go from 4T drives to 8T drives across the board is too > far in the future to worry about now. I have a bunch of 2s and have started > buying 4s, so thinking about how to handle that upgrade as the 2s age & > fail is on my mind. > > Advice and comments appreciated. > > Thanks > Thomas > > _______________________________________________ > TCLUG Mailing List - Minneapolis/St. Paul, Minnesota > tclug-list at mn-linux.org > http://mailman.mn-linux.org/mailman/listinfo/tclug-list > > > _______________________________________________ > TCLUG Mailing List - Minneapolis/St. Paul, Minnesota > tclug-list at mn-linux.org > http://mailman.mn-linux.org/mailman/listinfo/tclug-list > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mailman.mn-linux.org/pipermail/tclug-list/attachments/20150321/9c6d6205/attachment.html>