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  1. Core Server
  2. SERVER-51449

Mongodb unusually high iops during fsync mongoversion 3.2.10

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    Description

      we have mongodb with 1 primary and 2 secondaries. On primary node the disk write iops are spiking every minute and latencies go up.
      Looking further write iops seems like a bottle neck. so we reduced the fsyc time to 10 sec from 60 sec (default).

      It has helped us a lot but still the write iops on 60 qps update are around 1300 in every fsync.

      I did a test on another mongodb instance, on 1300 qps 363 iop we used during fsync (every 30 sec).

      the major difference between 2 mongos is the db size. IOPS in my mongo seems like an exceptional.

      I want to understand how db size impacts write iops during fsync. (In my understanding it should not have).
      What other factors are there in fsync write iops?
      what data should i be looking at?

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            edwin.zhou@mongodb.com Edwin Zhou
            c.programming.doubts@gmail.com maneesh bhunwal
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