This article, Amazon EBS Volumes with RAID Exam Tips provides a quick overview on the type of RAID options you can configure with your AWS EBS Volumes. As part of preparing for your AWS Certified Solutions Architect Associate exam, you may well have a question or two on the best RAID options available for your EBS volumes. It is also important to note that you can only use software RAID configurations with EBS Volumes.

EBS Volumes with RAID

You configure multiple EBS volumes in a RAID configuration to help increase performance and I/O above and beyond that which is provided by single EBS volume types on the AWS Platform. AWS enables you to use third-party tools to create software RAID configurations within your instances. Specifically, you have options to the following RAID configurations:

RAID 0 – This is where I/O performance is more important than fault tolerance. You can use RAID 0 configurations in scenarios where you are using heavy databases with perhaps mirroring and replication.
RAID 1 – This is where fault tolerance is more important than I/O performance and where you are running mission critical applications requiring fast recovery times and minimum downtime. With RAID 1 you get more data durability in addition to the replication features of the AWS cloud.

Important Exam Tip – RAID 5 and RAID 6 are not recommended for Amazon EBS because the parity write operations of these RAID modes consume some of the IOPS available to your volumes. Not only do RAID 5/6 provide fewer usable IOPS than RAID 0 configuration, the cost of implementing the solution also increases.

Snapshots of RAID Arrays

When you take a snapshot of an EBS volumes that are in use, the snapshot will exclude data that is cached by the application and OS. This can cause a problem when taking snapshots of RAID Arrays comprising of two or more EBS volumes wherein restoring from the snapshots can result in the degraded integrity of the array. You need to ensure that when you take the snapshot of a RAID array, not data is being written/read from those volumes. This means you need to ensure you are creating application consistent snapshots of the RAID array by stopping applications from writing to the Raid array and flushing all cache data to the disks.

You can do this by

Freezing the file system
Unmounting the RAID array
Shutdown the associated EC2 instance, take the snapshot and reboot the instance

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