Amazon SSD支持的EC2上的MongoDB

Question

We have mongodb sharded cluster currently deployed on EC2 instances in Amazon. These shards are also replica sets. The instances used are using EBS with IOPS provisioned.

We have about 30 million documents in a collection. Our queries count the whole collection that matches the filters. We have indexes on almost all of the query-able fields. This results to the RAM reaching 100% usage. Our working set exceeds the size of the RAM. We think that the slow response of our queries are caused by EBS being slow so we are thinking of migrating to the new SSD-backed instances.

C3 is available http://aws.typepad.com/aws/2013/11/a-generation-of-ec2-instances-for-compute-intensive-workloads.html

I2 is coming soon http://aws.typepad.com/aws/2013/11/coming-soon-the-i2-instance-type-high-io-performance-via-ssd.html

Our only concern is that SSD is ephemeral, meaning the data will be gone once the instance stops, terminates, or fails. How can we address this? How do we automate backups. Is it a good idea to migrate to SSD to improve the performance of our queries? Do we still need to set-up a sharded cluster?

Answer 1

Working with the ephemeral disks is a risk but if you have your replication setup correctly it shouldn't be a huge concern. I'm assuming you've setup a three node replica set correct? Also you have three nodes for your config servers?

I can speak of this from experience as the company I'm at has been setup this way. To help mitigate risk I'm moving towards a backup strategy that involved a hidden replica. With this setup I can shutdown the hidden replica set and one of the config servers (first having stopped balancing) and take a complete copy of the data files (replica and config server) and have a valid backup. If AWS went down on my availability zone I'd still have a daily backup available on S3 to restore from.

Hope this helps.