Hi Travis, Just one comment inline, in addition to what Sage wrote. On 05/01/2015 18:14, Travis Rhoden wrote: > Hi Loic and Wido, > > Loic - I agree with you that it makes more sense to implement the core > of the logic in ceph-disk where it can be re-used by other tools (like > ceph-deploy) or by administrators directly. There are a lot of > conventions put in place by ceph-disk such that ceph-disk is the best > place to undo them as part of clean-up. I'll pursue this with other > Ceph devs to see if I can get agreement on the best approach. > > At a high-level, ceph-disk has two commands that I think could have a > corollary -- prepare, and activate. > > Prepare will format and mkfs a disk/dir as needed to make it usable by Ceph. > Activate will put the resulting disk/dir into service by allocating an > OSD ID, creating the cephx key, and marking the init system as needed, > and finally starting the ceph-osd service. > > It seems like there could be two opposite commands that do the following: > > deactivate: > - set "ceph osd out" > - stop ceph-osd service if needed > - remove OSD from CRUSH map > - remove OSD cephx key > - deallocate OSD ID > - remove 'ready', 'active', and INIT-specific files (to Wido's point) > - umount device and remove mount point > > destroy: > - zap disk (removes partition table and disk content) > > A few questions I have from this, though. Is this granular enough? > If all the steps listed above are done in deactivate, is it useful? > Or are there usecases we need to cover where some of those steps need > to be done but not all? Deactivating in this case would be > permanently removing the disk from the cluster. If you are just > moving a disk from one host to another, Ceph already supports that > with no additional steps other than stop service, move disk, start > service. It is useful for test purposes. For instance, the puppet-ceph integration tests can use it to ensure the osd is removed properly with no knowledge of the details. > Is "destroy" even necessary? It's really just zap at that point, > which already exists. It only seems necessary to me if we add extra > functionality, like the ability to do a wipe of some kind first. If > it is just zap, you could call zap separate or with --zap as an option > to deactivate. > > > And all of this would need to be able to fail somewhat gracefully, as > you would often be dealing with dead/failed disks that may not allow > these commands to run successfully. That's why I'm wondering if it > would be best to break the steps currently in "deactivate" into two > commands -- (1) deactivate: which would deal with commands specific to > the disk (osd out, stop service, remove marker files, umount) and (2) > remove: which would undefine the OSD within the cluster (remove from > CRUSH, remove cephx key, deallocate OSD ID). > > I'm mostly talking out loud here. Looking for more ideas, input. :) > > - Travis > > > On Sun, Jan 4, 2015 at 6:07 AM, Wido den Hollander <wido@xxxxxxxx> wrote: >> On 01/02/2015 10:31 PM, Travis Rhoden wrote: >>> Hi everyone, >>> >>> There has been a long-standing request [1] to implement an OSD >>> "destroy" capability to ceph-deploy. A community user has submitted a >>> pull request implementing this feature [2]. While the code needs a >>> bit of work (there are a few things to work out before it would be >>> ready to merge), I want to verify that the approach is sound before >>> diving into it. >>> >>> As it currently stands, the new feature would do allow for the following: >>> >>> ceph-deploy osd destroy <host> --osd-id <id> >>> >>> From that command, ceph-deploy would reach out to the host, do "ceph >>> osd out", stop the ceph-osd service for the OSD, then finish by doing >>> "ceph osd crush remove", "ceph auth del", and "ceph osd rm". Finally, >>> it would umount the OSD, typically in /var/lib/ceph/osd/... >>> >> >> Prior to the unmount, shouldn't it also clean up the 'ready' file to >> prevent the OSD from starting after a reboot? >> >> Although it's key has been removed from the cluster it shouldn't matter >> that much, but it seems a bit cleaner. >> >> It could even be more destructive, that if you pass --zap-disk to it, it >> also runs wipefs or something to clean the whole disk. >> >>> >>> Does this high-level approach seem sane? Anything that is missing >>> when trying to remove an OSD? >>> >>> >>> There are a few specifics to the current PR that jump out to me as >>> things to address. The format of the command is a bit rough, as other >>> "ceph-deploy osd" commands take a list of [host[:disk[:journal]]] args >>> to specify a bunch of disks/osds to act on at one. But this command >>> only allows one at a time, by virtue of the --osd-id argument. We >>> could try to accept [host:disk] and look up the OSD ID from that, or >>> potentially take [host:ID] as input. >>> >>> Additionally, what should be done with the OSD's journal during the >>> destroy process? Should it be left untouched? >>> >>> Should there be any additional barriers to performing such a >>> destructive command? User confirmation? >>> >>> >>> - Travis >>> >>> [1] http://tracker.ceph.com/issues/3480 >>> [2] https://github.com/ceph/ceph-deploy/pull/254 >>> -- >>> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in >>> the body of a message to majordomo@xxxxxxxxxxxxxxx >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >> >> >> -- >> Wido den Hollander >> 42on B.V. >> Ceph trainer and consultant >> >> Phone: +31 (0)20 700 9902 >> Skype: contact42on > -- > To unsubscribe from this list: send the line "unsubscribe ceph-devel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- Loïc Dachary, Artisan Logiciel Libre
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