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Given that S3 is 99.999999999% durability [1], what is the equivalent figure for DynamoDB?
[1] http://aws.amazon.com/s3/
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DynamoDB automatically scales throughput capacity to meet workload demands, and partitions and repartitions your data as your table size grows. Also, DynamoDB synchronously replicates data across three facilities in an AWS Region, giving you high availability and data durability.
The data is eventually consistent across all storage locations, usually within one second or less. DynamoDB supports eventually consistent and strongly consistent reads. When you read data from a DynamoDB table, the response might not reflect the results of a recently completed write operation.
DynamoDB uses eventually consistent reads, unless you specify otherwise. Read operations (such as GetItem , Query , and Scan ) provide a ConsistentRead parameter. If you set this parameter to true, DynamoDB uses strongly consistent reads during the operation.
This question implies something that is incorrect. Though S3 has an SLA (aws.amazon.com/s3-sla) that SLA references availability (99.9%) but has no reference to durability, or the loss of objects in S3.
The 99.999999999% durability figure comes from Amazon's estimate of what S3 is designed to achieve and there is no related SLA.
Note that Amazon S3 is designed for 99.99% availability but the SLA kicks in at 99.9%.
There is no current DynamoDB SLA from Amazon, nor am I aware of any published figures from Amazon on the expected or designed durability of data in DynamoDB. I would suspect that it is less than S3 given the nature, relative complexities, and goals of the two systems (i.e., S3 is designed to simply store data objects very, very safely; DynamoDB is designed to provide super-fast reads and writes in a scalable distributed database while also trying to keep your data safe).
Amazon talks about customers backing up DynamoDB to S3 using MapReduce. They also say that some customers back up DynamoDB using Redshift, which has DynamoDB compatibility built in. I additionally recommend backing up to an off-AWS store to remove the single point of failure that is your AWS account.
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Although the DynamoDB FAQ doesn't use the exact same wording as you can see from my highlights below both DynamoDB & S3 are designed to be fault tolerant, with data stored in three facilities.
I wasn't able to find exact figures reported anywhere, but from the information I did have it looks like DynamoDB is pretty durable (on par with S3), although that won't stop it from having service interruptions from time to time. See this link:
http://www.forbes.com/sites/kellyclay/2013/02/20/amazons-aws-experiencing-problems-again/
S3 FAQ: http://aws.amazon.com/s3/faqs/#How_is_Amazon_S3_designed_to_achieve_99.999999999%_durability
Q: How durable is Amazon S3? Amazon S3 is designed to provide 99.999999999% durability of objects over a given year.
In addition, Amazon S3 is designed to sustain the concurrent loss of data in two facilities.
Also Note: The "99.999999999%" figure for S3 is over a given year.
DynamoDB FAQ: http://aws.amazon.com/dynamodb/faqs/#Is_there_a_limit_to_how_much_data_I_can_store_in_Amazon_DynamoDB
Scale, Availability, and Durability
Q: How highly available is Amazon DynamoDB?
The service runs across Amazon’s proven, high-availability data centers. The service replicates data across three facilities in an AWS Region to provide fault tolerance in the event of a server failure or Availability Zone outage.
Q: How does Amazon DynamoDB achieve high uptime and durability?
To achieve high uptime and durability, Amazon DynamoDB synchronously replicates data across three facilities within an AWS Region.
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