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We have a 3.2.13 Mongodb replica set with WiredTiger on AWS.

We are observing a strange behaviour: when stopping and starting the mongod service, the start time is about 10 minutes, but when stopping the mongod service, then replicating the data disk to a new AWS instance, and restarting on that machine, the start time is about 2 hours.

What may be the cause for this?

  • Have you checked mongod.log file? What it says during that startup? tail -f /var/log/mongodb/mongod.log – JJussi Jan 3 '18 at 14:46
  • @JJussi it doesn't show anything after printing 'options' and 'wiredtiger_open config'. – David Resnick Jan 4 '18 at 13:18
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It looks like the initial slowness is because the EBS volume (which is restored from snapshot) is being initialized during the service startup.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-initialize.html

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