Durability and Availability - AWS Storage Services Overview

Durability and Availability

Amazon EBS volumes are designed to be highly available and reliable. EBS volume data is replicated across multiple servers in a single Availability Zone to prevent the loss of data from the failure of any single component. Taking snapshots of your EBS volumes increases the durability of the data stored on your EBS volumes. EBS snapshots are incremental, point-in-time backups, containing only the data blocks changed since the last snapshot. EBS volumes are designed for an annual failure rate (AFR) of between 0.1 and 0.2 percent, where failure refers to a complete or partial loss of the volume, depending on the size and performance of the volume. This means, if you have 1,000 EBS volumes over the course of a year, you can expect unrecoverable failures with 1 or 2 of your volumes. This AFR makes EBS volumes 20 times more reliable than typical commodity disk drives, which fail with an AFR of around 4 percent. Despite these very low EBS AFR numbers, we still recommend that you create snapshots of your EBS volumes to improve the durability of your data. The Amazon EBS snapshot feature makes it easy to take application-consistent backups of your data. For more information on EBS durability, see the Amazon EBS Availability and Durability section of the Amazon EBS Product Details page.

To maximize both durability and availability of Amazon EBS data, you should create snapshots of your EBS volumes frequently. (For application-consistent backups, we recommend briefly pausing any write operations to the volume, or unmounting the volume, while you issue the snapshot command. You can then safely continue to use the volume while the snapshot is pending completion.) All EBS volume types offer durable snapshot capabilities and are designed for 99.999 percent availability. If your EBS volume does fail, all snapshots of that volume remain intact, and you can recreate your volume from the last snapshot point. Because an EBS volume is created in a particular Availability Zone, the volume will be unavailable if the Availability Zone itself is unavailable. A snapshot of a volume, however, is available across all of the Availability Zones within a Region, and you can use a snapshot to create one or more new EBS volumes in any Availability Zone in the region. EBS snapshots can also be copied from one Region to another, and can easily be shared with other user accounts. Thus, EBS snapshots provide an easy-to-use disk clone or disk image mechanism for backup, sharing, and disaster recovery.