Use the following link, it should give an idea about pg_number. http://ceph.com/pgcalc/ Number of PGs/OSd has implication on number of TCP connection in the system along with some resources on cpu/memory. So, if you have lots of PG/OSD it may degrade performance, I think mainly because of extensive number of TCP connection specially if you have pretty decent high end node and not worrying about cpu/memory. Basically, ~200 PGs/OSD we should be targeting for. On the other hand, very less PG/OSD will hurt parallelism because Ceph will not allow multiple operation on a PG to go in parallel. I am not sure if data distribution will affect that much (considering you have pgs more than your OSDs :-) ) , but I must admit that I never tried with very few Pgs... Thanks & Regards Somnath -----Original Message----- From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Francois Lafont Sent: Friday, November 13, 2015 4:34 AM To: ceph-users@xxxxxxxxxxxxxx Subject: Re: about PG_Number Hi, On 13/11/2015 09:13, Vickie ch wrote: > If you have a large amount of OSDs but less pg number. You will find > your data write unevenly. > Some OSD have no change to write data. > In the other side, pg number too large but OSD number too small that > have a chance to cause data lost. Data lost, are you sure? Personally, I would have said: few PG/OSDs lot of PG/OSDs ------------------------------------> * Data distribution less envenly * Good balanced distribution of data * Use less CPU and RAM * Use lot of CPU and RAM No? François Lafont _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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