I also would be interested in how bcache or flashcache would integrate.
On Mon, Oct 7, 2013 at 11:34 AM, Martin Catudal <mcatu...@metanor.ca> wrote:
> Thank's Mike,
> Kyle Bader suggest me also to use my large SSD (900 GB) as cache
> drive using "bcache" or "flashcache".
> Since I have already plan to use SSD for my journal, I would certainly
> use also SSD as cache drive in addition.
>
> I will have to read documentation about "bcache" and his integration
> with Ceph.
>
> Martin
>
> Martin Catudal
> Responsable TIC
> Ressources Metanor Inc
> Ligne directe: (819) 218-2708
>
> Le 2013-10-07 11:25, Mike Lowe a écrit :
> > Based on my experience I think you are grossly underestimating the
> expense and frequency of flushes issued from your vm's. This will be
> especially bad if you aren't using the async flush from qemu >= 1.4.2 as
> the vm is suspended while qemu waits for the flush to finish. I think your
> best course of action until the caching pool work is completed (I think I
> remember correctly that this is currently in development) is to either use
> the ssd's as large caches with bcache or to use them for journal devices.
> I'm sure there are some other more informed opinions out there on the best
> use of ssd's in a ceph cluster and hopefully they will chime in.
> >
> > On Oct 6, 2013, at 9:23 PM, Martin Catudal <mcatu...@metanor.ca> wrote:
> >
> >> Hi Guys,
> >> I read all Ceph documentation more than twice. I'm now very
> >> comfortable with all the aspect of Ceph except for the strategy of using
> >> my SSD and HDD.
> >>
> >> Here is my reflexion
> >>
> >> I've two approach in my understanding about use fast SSD (900 GB) for my
> >> primary storage and huge but slower HDD (4 TB) for replicas.
> >>
> >> FIRST APPROACH
> >> 1. I can use PG with cache write enable as my primary storage that's
> >> goes on my SSD and let replicas goes on my 7200 RPM.
> >> With the cache write enable, I will gain performance for my VM
> >> user machine in VDI environment since Ceph client will not have to wait
> >> for the replicas write confirmation on the slower HDD.
> >>
> >> SECOND APPROACH
> >> 2. Use pools hierarchies and let's have one pool for the SSD as primary
> >> and lets the replicas goes to a second pool name platter for HDD
> >> replication.
> >> As explain in the Ceph documentation
> >> rule ssd-primary {
> >> ruleset 4
> >> type replicated
> >> min_size 5
> >> max_size 10
> >> step take ssd
> >> step chooseleaf firstn 1 type host
> >> step emit
> >> step take platter
> >> step chooseleaf firstn -1 type host
> >> step emit
> >> }
> >>
> >> At this point, I could not figure out what approach could have the most
> >> advantage.
> >>
> >> Your point of view would definitely help me.
> >>
> >> Sincerely,
> >> Martin
> >>
> >> --
> >> Martin Catudal
> >> Responsable TIC
> >> Ressources Metanor Inc
> >> Ligne directe: (819) 218-2708
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> >> ceph-users@lists.ceph.com
> >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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