Those numbers look right for a pool only containing 10% of your data. Now continue to calculate the pg counts for the remaining 90% of your data.
On Wed, Feb 27, 2019, 12:17 PM Krishna Venkata <kvenkata...@gmail.com> wrote: > Greetings, > > > I am having issues in the way PGs are calculated in > https://ceph.com/pgcalc/ [Ceph PGs per Pool Calculator ] and the formulae > mentioned in the site. > > Below are my findings > > The formula to calculate PGs as mentioned in the https://ceph.com/pgcalc/ > : > > 1. Need to pick the highest value from either of the formulas > > *(( Target PGs per OSD ) x ( OSD # ) x ( %Data ))/(size)* > > Or > > *( OSD# ) / ( Size )* > > 2. The output value is then rounded to the nearest power of 2 > > 1. If the nearest power of 2 is more than 25% below the original > value, the next higher power of 2 is used. > > > > Based on the above procedure, we calculated PGs for 25, 32 and 64 OSDs > > *Our Dataset:* > > *%Data:* 0.10 > > *Target PGs per OSD:* 100 > > *OSDs* 25, 32 and 64 > > > > *For 25 OSDs* > > > > (100*25* (0.10/100))/(3) = 0.833 > > > > ( 25 ) / ( 3 ) = 8.33 > > > > 1. Raw pg num 8.33 ( Since we need to pick the highest of (0.833, 8.33)) > > 2. max pg 16 ( For, 8.33 the nearest power of 2 is 16) > > 3. 16 > 2.08 ( 25 % of 8.33 is 2.08 which is more than 25% the power of 2) > > > > So 16 PGs > > ü GUI Calculator gives the same value and matches with Formula. > > > > *For 32 OSD* > > > > (100*32*(0.10/100))/3 = 1.066 > > ( 32 ) / ( 3 ) = 10.66 > > > > 1. Raw pg num 10.66 ( Since we need to pick the highest of (1.066, 10.66)) > > 2. max pg 16 ( For, 10.66 the nearest power of 2 is 16) > > 3. 16 > 2.655 ( 25 % of 10.66 is 2.655 which is more than 25% the power > of 2) > > > > So 16 PGs > > û GUI Calculator gives different value (32 PGs) which doesn’t match with > Formula. > > > > *For 64 OSD* > > > > (100 * 64 * (0.10/100))/3 = 2.133 > > ( 64 ) / ( 3 ) 21.33 > > > > 1. Raw pg num 21.33 ( Since we need to pick the highest of (2.133, 21.33)) > > 2. max pg 32 ( For, 21.33 the nearest power of 2 is 32) > > 3. 32 > 5.3325 ( 25 % of 21.33 is 5.3325 which is more than 25% the power > of 2) > > > > So 32 PGs > > û GUI Calculator gives different value (64 PGs) which doesn’t match with > Formula. > > > > We checked the PG calculator logic from [ > https://ceph.com/pgcalc_assets/pgcalc.js ] which is not matching from > above formulae. > > > > Can someone Guide/reference us to correct formulae to calculate PGs. > > > > Thanks in advance. > > > > Regards, > > Krishna Venkata > _______________________________________________ > ceph-users mailing list > ceph-users@lists.ceph.com > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com >
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