To put this in context, the goal here is to kill ceph-disk in mimic. One proposal is to make it so new OSDs can *only* be deployed with LVM, and old OSDs with the ceph-disk GPT partitions would be started via ceph-volume support that can only start (but not deploy new) OSDs in that style.
Is the LVM-only-ness concerning to anyone? Looking further forward, NVMe OSDs will probably be handled a bit differently, as they'll eventually be using SPDK and kernel-bypass (hence, no LVM). For the time being, though, they would use LVM. On Fri, 6 Oct 2017, Alfredo Deza wrote: > Now that ceph-volume is part of the Luminous release, we've been able > to provide filestore support for LVM-based OSDs. We are making use of > LVM's powerful mechanisms to store metadata which allows the process > to no longer rely on UDEV and GPT labels (unlike ceph-disk). > > Bluestore support should be the next step for `ceph-volume lvm`, and > while that is planned we are thinking of ways to improve the current > caveats (like OSDs not coming up) for clusters that have deployed OSDs > with ceph-disk. > > --- New clusters --- > The `ceph-volume lvm` deployment is straightforward (currently > supported in ceph-ansible), but there isn't support for plain disks > (with partitions) currently, like there is with ceph-disk. > > Is there a pressing interest in supporting plain disks with > partitions? Or only supporting LVM-based OSDs fine? Perhaps the "out" here is to support a "dir" option where the user can manually provision and mount an OSD on /var/lib/ceph/osd/*, with 'journal' or 'block' symlinks, and ceph-volume will do the last bits that initialize the filestore or bluestore OSD from there. Then if someone has a scenario that isn't captured by LVM (or whatever else we support) they can always do it manually? > --- Existing clusters --- > Migration to ceph-volume, even with plain disk support means > re-creating the OSD from scratch, which would end up moving data. > There is no way to make a GPT/ceph-disk OSD become a ceph-volume one > without starting from scratch. > > A temporary workaround would be to provide a way for existing OSDs to > be brought up without UDEV and ceph-disk, by creating logic in > ceph-volume that could load them with systemd directly. This wouldn't > make them lvm-based, nor it would mean there is direct support for > them, just a temporary workaround to make them start without UDEV and > ceph-disk. > > I'm interested in what current users might look for here,: is it fine > to provide this workaround if the issues are that problematic? Or is > it OK to plan a migration towards ceph-volume OSDs? IMO we can't require any kind of data migration in order to upgrade, which means we either have to (1) keep ceph-disk around indefinitely, or (2) teach ceph-volume to start existing GPT-style OSDs. Given all of the flakiness around udev, I'm partial to #2. The big question for me is whether #2 alone is sufficient, or whether ceph-volume should also know how to provision new OSDs using partitions and no LVM. Hopefully not? sage _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
