Thanks, I’ll take a look at osd_internals. Are you saying that a cache tier —> EC Pool is good enough? What if any is the downside to using a cache tier ontop of an EC pool? I assume that the size of cache is going to be important, and so is the migration algorithm between the cache tier and the backing tier.
> On Jan 30, 2015, at 10:49 AM, Samuel Just <sam.j...@inktank.com> wrote: > > This would need to be a new backend, and it's going to be a massive > amount of work. You want to start by reading and understanding all of > the docs in osd_internals. I also suspect you'll get a lot of what > you need from using a replicated cache in front of an EC pool. > -Sam > > On Fri, Jan 30, 2015 at 10:00 AM, Bassam Tabbara > <bassamtabb...@hotmail.com> wrote: >> I’d like to explore adding a new EC pool type as you suggest. The idea is to >> have RBD sit on-top of a fully functional EC backend. Just as with RAID6 >> arrays today some applications are aware of the read-modify-write penalty >> and they could optimize for it. >> >> I’m new to ceph, so if you can point me in the right direction I would >> appreciate it. Do you think this is something that could be implemented as a >> modification to the existing ECBackend or is this a new backend. I’m happy >> to jump on a quick call if it makes things easier. >> >>> On Jan 30, 2015, at 8:59 AM, Samuel Just <sam.j...@inktank.com> wrote: >>> >>> Basically, it's an architectural choice: >>> >>> https://github.com/ceph/ceph/blob/master/doc/dev/osd_internals/erasure_coding/pgbackend.rst#client-writes >>> >>> If we wanted to support partial writes, we'd probably want to >>> introduce a second EC pool type with different tradeoffs. Note, you >>> can get slow partial writes on an EC pool by placing a replicated >>> cache in front. >>> -Sam >>> >>> On Fri, Jan 30, 2015 at 8:36 AM, Bassam Tabbara >>> <bassamtabb...@hotmail.com> wrote: >>>> Hello, >>>> >>>> I realize that the EC Backend does not support all operations like partial >>>> writes, truncate, and others. I’d like to understand whether adding the >>>> missing operations is something that is architecturally possible, or if >>>> this is a limitation of the architecture / approach. Can someone shed some >>>> light on this? >>>> >>>> I realize that partial writes are going to be slow/inefficient on an EC >>>> backend compared to a replicated backend. >>>> >>>> Thanks! >>>> Bassam-- >>>> 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
