Amazon EFS provides file storage in the AWS Cloud. With Amazon EFS, you can create a file system, mount the file system on an Amazon EC2 instance, and then read and write data to and from your file system.

You can mount an Amazon EFS file system in your VPC, through the Network File System versions 4.0 and 4.1 (NFSv4) protocol. We recommend using a current generation Linux NFSv4.1 client, such as those found in the latest Amazon Linux, Redhat, and Ubuntu AMIs, in conjunction with the Amazon EFS Mount Helper.

 An Amazon Elastic Block Store (EBS) volume can only be attached to a single instance and cannot be shared.

Amazon S3 is an object storage system that is accessed via REST API not file-level protocols. It cannot be attached to EC2 instances.

An EC2 instance store is an ephemeral storage volume that is local to the server on which the instances runs and is not persistent. It is accessed via block protocols and also cannot be shared between instances.

."file storage layer that can be shared between multiple EC2 instances." - clearly indicates towards EFS as it is a file storage system & can be shared multiple EC2 instances, which isn't possible with other options.

Solutions Architect should use the SCT to extract and load to Snowball Edge and then AWS DMS in the AWS Cloud.

 Direct Connect connections can take several weeks to implement.

It’s unlikely that compression is going to make the difference and the company want to avoid the internet link as stated in the scenario.

Larger data migrations with AWS DMS can include many terabytes of information. This process can be cumbersome due to network bandwidth limits or just the sheer amount of data. AWS DMS can use Snowball Edge and Amazon S3 to migrate large databases more quickly than by other methods.

When you’re using an Edge device, the data migration process has the following stages:

• You use the AWS Schema Conversion Tool (AWS SCT) to extract the data locally and move it to an Edge device.
• You ship the Edge device or devices back to AWS.
• After AWS receives your shipment, the Edge device automatically loads its data into an Amazon S3 bucket.
• AWS DMS takes the files and migrates the data to the target data store. If you are using change data capture (CDC), those updates are written to the Amazon S3 bucket and then applied to the target data store.

• "database running on-premises must be migrated to Amazon DynamoDB" - clearly indicates towards AWS Database Migration Service (DMS).

• "too large to migrate over the company’s limited internet bandwidth" - then we have to set up an AWS Direct Connect

• Maintenance windows are configured to allow DB instance modifications to take place such as scaling and software patching. Some operations require the DB instance to be taken offline briefly and this includes security patching

Promoting a Read Replica doesn't require maintainence window.

Updating DB parameter groups doesn't require maintainence window.

 Selecting the Multi-AZ feature doesn't require maintainence window.

• Maintenance windows are configured to allow DB instance modifications to take place such as scaling and software patching. Some operations require the DB instance to be taken offline briefly and this includes security patching.
• Enabling Multi-AZ, promoting a Read Replica and updating DB parameter groups are not events that take place during a maintenance window