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
>> _______________________________________________
>> ceph-users mailing list
>> ceph-users@lists.ceph.com
>> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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