In terms of making something work really quickly, one approach would be to base off the existing POSIX translator, use a local FS backed by an RBD volume for the metadata, and store the file content directly using librados. That would avoid the need to invent a way to map filesystem-style metadata to librados calls, while still getting reasonably efficient data operations through to rados. I would doubt this would be very slick, but it could be a fun hack! John On Mon, May 5, 2014 at 4:21 PM, Jeff Darcy <jdarcy@xxxxxxxxxx> wrote: > > Now that we're all one big happy family, I've been mulling over > different ways that the two technology stacks could work together. One > idea would be to use some of the GlusterFS upper layers for their > interface and integration possibilities, but then falling down to RADOS > instead of GlusterFS's own distribution and replication. I must > emphasize that I don't necessarily think this is The Right Way for > anything real, but I think it's an important experiment just to see what > the problems are and how well it performs. So here's what I'm thinking. > > For the Ceph folks, I'll describe just a tiny bit of how GlusterFS > works. The core concept in GlusterFS is a "translator" which accepts > file system requests and generates file system requests in exactly the > same form. This allows them to be stacked in arbitrary orders, moved > back and forth across the server/client divide, etc. There are several > broad classes of translators: > > * Some, such as FUSE or GFAPI, inject new requests into the translator > stack. > > * Some, such as "posix", satisfy requests by calling a server-local FS. > > * The "client" and "server" translators together get requests from one > machine to another. > > * Some translators *route* requests (one in to one of several out). > > * Some translators *fan out* requests (one in to all of several out). > > * Most are one in, one out, to add e.g. locks or caching etc. > > Of particular interest here are the DHT (routing/distribution) and AFR > (fan-out/replication) translators, which mirror functionality in RADOS. > My idea is to cut out everything from these on below, in favor of a > translator based on librados instead. How this works is pretty obvious > for file data - just read and write to RADOS objects instead of to > files. It's a bit less obvious for metadata, especially directory > entries. One really simple idea is to store metadata as data, in some > format defined by the translator itself, and have it handle the > read/modify/write for adding/deleting entries and such. That would be > enough to get some basic performance tests done. A slightly more > sophisticated idea might be to use OSD class methods to do the > read/modify/write, but I don't know much about that mechanism so I'm not > sure that's even feasible. > > This is not something I'm going to be working on as part of my main job, > but I'd like to get the experiment started in some of my "spare" time. > Is there anyone else interested in collaborating, or are there any other > obvious ideas I'm missing? > -- > 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 -- 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
