Thursday, 5 February 2015

Q: How do I select the right number of instances for my cluster?

The number of instances to use in your cluster is application-dependent and should be based on both the amount of resources required to store and process your data and the acceptable amount of time for your job to complete. As a general guideline, we recommend that you limit 60% of your disk space to storing the data you will be processing, leaving the rest for intermediate output. Hence, given 3x replication on HDFS, if you were looking to process 5 TB on m1.xlarge instances, which have 1,690 GB of disk space, we recommend your cluster contains at least (5 TB * 3) / (1,690 GB * .6) = 15 m1.xlarge core nodes. You may want to increase this number if your job generates a high amount of intermediate data or has significant I/O requirements. You may also want to include additional task nodes to improve processing performance. See Amazon EC2 Instance Types for details on local instance storage for each instance type configuration.

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