You`re running a financial application on an EC2 instance. Data stored in the EBS volumes is critical and you want to make it fault-tolerant. Which of the following options provides the most fault-tolerant configuration?

Answer options:

A.Mirror the data using RAID 1 configuration, which provides fault tolerance on EBS volumes.
B.Nothing is required since EBS volumes are durability backed up to additional hardware in the same availability zone.
C.Mirror the data using RAID 5 configuration to improve the I/O performance on EBS volumes.
D.Stripe multiple EBS volumes together with RAID 0, which provides fault tolerance on EBS volumes.

Answer – A
Option A is CORRECT because, as mentioned above, RAID 1 configuration maintains the exact copy of the data (via mirroring) in a backup EBS volume that can be used in case of the failure of the main volume, providing redundancy and fault tolerance.
Option B is incorrect because, although each Amazon EBS volume is automatically replicated within its Availability Zone, it is done so to protect it from any component failure from the AWS side. It does not withstand any failures at the user level. It is the user`s responsibility to replicate the data that is stored on the EBS volume. 
EBS volumes are not automatically backed up to additional hardware in the same availability zone. You will need to set up your backup strategy when using EBS volumes. 
EBS Snapshot Doc: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/EBSSnapshots.html
Option C is incorrect because RAID 5 does not improve the fault tolerance. RAID 5 and RAID 6 are not recommended for Amazon EBS because these RAID modes` parity write operations consume some of the IOPS available to your volumes.
Option D is incorrect because RAID 0 configuration helps improve the performance but does not provide redundancy or mirroring of the data across disks. As a result of having data striped across all disks, any failure will result in total data loss. 
More information on RAID Configurations with EBS volumes:
As per the AWS documentation, it is clearly given to use RAID 1 configuration for fault tolerance of EBS volumes.
 With Amazon EBS, you can use any of the standard RAID configurations that you can use with a traditional bare metal server, as long as the operating system for your instance supports that particular RAID configuration. This is because all RAID is accomplished at the software level. For greater I/O performance than you can achieve with a single volume, RAID 0 can stripe multiple volumes together; for on-instance redundancy, RAID 1 can mirror two volumes together.
For more information on RAID configuration, please visit the below URL-
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/raid-config.html