One of Ceph's design tentpoles is *avoiding* a central metadata lookup table. The Ceph MDS maintains a filesystem hierarchy but doesn't really handle the sort of thing you're talking about, either. If you want some kind of lookup, you'll need to build it yourself — although you could make use of some RADOS features to do it, if you really wanted to. (For instance, depending on scale you could keep an index of objects in an omap somewhere.) -Greg Software Engineer #42 @ http://inktank.com | http://ceph.com
On Tue, Jul 15, 2014 at 10:11 AM, Shayan Saeed <shayansaee...@gmail.com> wrote: > Well I did end up putting the data in different pools for custom > placement. However, I run into trouble during retrieval. The messy way > is to query every pool to check where the data is stored. This > requires many round trips to machines in the far off racks. Is it > possible this information is contained within a centralized sort of > metadata server? I understand that for simple object store MDS is not > used but is there a way to utilize it for faster querying? > > Regards, > Shayan Saeed > > > On Tue, Jun 24, 2014 at 11:37 AM, Gregory Farnum <g...@inktank.com> wrote: >> On Tue, Jun 24, 2014 at 8:29 AM, Shayan Saeed <shayansaee...@gmail.com> >> wrote: >>> Hi, >>> >>> CRUSH placement algorithm works really nice with replication. However, >>> with erasure code, my cluster has some issues which require making >>> changes that I cannot specify with CRUSH maps. >>> Sometimes, depending on the type of data, I would like to place them >>> on different OSDs but in the same pool. >> >> Why do you want to keep the data in the same pool? >> >>> >>> I realize that to disable the CRUSH placement algorithm and replacing >>> it with my own custom algorithm, such as random placement algo or any >>> other, I have to make changes in the source code. I want to ask if >>> there is an easy way to do this without going into every code file and >>> looking where the mapping from objects to PG is done and changing >>> that. Is there some configuration option which disables crush and >>> points to my own placement algo file for doing custom placement. >> >> What you're asking for really doesn't sound feasible, but the thing >> that comes closest would probably be resurrecting the "pg preferred" >> mechanisms in CRUSH and the Ceph codebase. You'll have to go back >> through the git history to find it, but once upon a time we supported >> a mechanism that let you specify a specific OSD you wanted a >> particular object to live on, and then it would place the remaining >> replicas using CRUSH. >> -Greg >> Software Engineer #42 @ http://inktank.com | http://ceph.com >> >>> >>> Let me know about the most neat way to go about it. Appreciate any >>> help I can get. >>> >>> Regards, >>> Shayan Saeed >>> Research Assistant, Systems Research Lab >>> University of Illinois Urbana-Champaign >>> -- >>> To unsubscribe from this list: send the line "unsubscribe ceph-devel" in >>> the body of a message to majord...@vger.kernel.org >>> 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
