Re: Best layout for SSD & SAS OSDs

German Anders <ganders@xxxxxxxxxxxx> · Fri, 4 Sep 2015 13:17:34 -0300

Thanks a lot Nick, regarding the power feeds, we only had two circuits for all the racks, so I'll to do in the crush the "rack" bucket and separate the osd servers on the rack buckets, then regarding the SSD pools, I've installed the hammer version and wondering to upgrade to Infernalis v9.0.3 and apply the SSD cache, or stay on Hammer and do the SSD pools and maybe left two 800GB SSD for later used as Cache (1.6TB per OSD server), do you have a crushmap example for this type of config?

Thanks a lot,

Best regards,

German

2015-09-04 13:10 GMT-03:00 Nick Fisk <nick@xxxxxxxxxx>:
Hi German,

Are the power feeds completely separate (ie 4 feeds in total), or just each rack has both feeds? If it’s the latter I don’t see any benefit from including this into the crushmap and would just create a “rack” bucket. Also assuming your servers have dual PSU’s, this also changes the power failure scenarios quite a bit as well.

In regards to the pools, unless you know your workload will easily fit into a cache pool with room to spare, I would suggest not going down that route currently. Performance in many cases can actually end up being worse if you end up doing a lot of promotions.

*However* I’ve been doing a bit of testing with the current master and there are a lot of improvements around cache tiering that are starting to have a massive improvement on performance. If you can get by with just the SAS disks for now and make a more informed decision about the cache tiering when Infernalis is released then that might be your best bet.

Otherwise you might just be best using them as a basic SSD only Pool.

Nick

From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of German Anders
Sent: 04 September 2015 16:30
To: ceph-users <ceph-users@xxxxxxxxxxxxxx>
Subject:  Best layout for SSD & SAS OSDs

Hi cephers,
   I've the following scheme:
7x OSD servers with:
    4x 800GB SSD Intel DC S3510 (OSD-SSD)
    3x 120GB SSD Intel DC S3500 (Journals)
    5x 3TB SAS disks (OSD-SAS)
The OSD servers are located on two separate Racks with two power circuits each.
   I would like to know what is the best way to implement this.. use the 4x 800GB SSD like a SSD-pool, or used them us a Cache pool? or any other suggestion? Also any advice for the crush design?
Thanks in advance,    

German

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