On Wed, Aug 22, 2012 at 9:33 AM, Sage Weil <sage@xxxxxxxxxxx> wrote: > On Wed, 22 Aug 2012, Atchley, Scott wrote: >> On Aug 22, 2012, at 10:46 AM, Florian Haas wrote: >> >> > On 08/22/2012 03:10 AM, Sage Weil wrote: >> >> I pushed a branch that changes some of the crush terminology. Instead of >> >> having a crush type called "pool" that requires you to say things like >> >> "pool=default" in the "ceph osd crush set ..." command, it uses "root" >> >> instead. That hopefully reinforces that it is a tree/hierarchy. >> >> >> >> There is also a patch that changes "bucket" to "node" throughout, since >> >> bucket is a term also used by radosgw. >> >> >> >> Thoughts? I think the main pain in making this transition is that old >> >> clusters have maps that have a type 'pool' and new ones won't, and the >> >> docs will need to walk people through both... >> > >> > "pool" in a crushmap being completely unrelated to a RADOS pool is >> > something that I've heard customers/users report as confusing, as well. >> > So changing that is probably a good thing. Naming it "root" is probably >> > a good choice as well, as it happens to match >> > http://ceph.com/wiki/Custom_data_placement_with_CRUSH. >> > >> > As for changing "bucket" to node... a "node" is normally simply a >> > physical server (at least in HA terminology, which many potential Ceph >> > users will be familiar with), and CRUSH uses "host" for that. So that's >> > another recipe for confusion. How about using something super-generic, >> > like "element" or "item"? >> > >> > Cheers, >> > Florian >> >> My guess is that he is trying to use data structure tree nomenclature >> (root, node, leaf). I agree that node is an overloaded term (as is >> pool). > > Yeah... > >> As for an alternative to bucket which indicates the item is a >> collection, what about subtree or branch? > > I think fixing the overloading of 'pool' in the default crush map is the > biggest pain point. I can live with crush 'buckets' staying the same (esp > since that's what the papers and code use pervasively) if we can't come up > with a better option. I'm definitely most interested in replacing "pool", and "root" works for that in my mind. RGW buckets live at a sufficiently different level that I think people are unlikely to be confused — and "bucket" is actually a good name for what they are (I'm open to better ones, but I don't think that "node" qualifies). > On the pool part, though, the challenge is how to transition. Existing > clusters have maps that use 'pool', and new clusters will use 'root' (or > whatever). Some options: > > - document both. this kills much of the benefit of switching, but is > probably inevitable since people will be running different versions. > - make the upgrade process transparently rename the type. this lets > all the tools use the new names. > - make the tools silently translate old names to new names. this is > kludgey in that it makes the code make assumptions about the names of > the data it is working with, but would cover everyone except those who > created their own crush maps from scratch. > - ? I would go with option two, and only document the new options — I wouldn't be surprised if the number of people who had changed those was zero. Anybody who has done so can certainly be counted on to pay enough attention that a line note "changed CRUSH names (see here if you customized your map)" would be sufficient, right? -Greg -- 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
