What is the problem and a valid solution?

You have launched an EC2 instance with four (4) 500 GB EBS Provisioned IOPS volumes
attached. The EC2 instance is EBS-Optimized and supports 500 Mbps throughput between EC2
and EBS. The four EBS volumes are configured as a single RAID 0 device, and each Provisioned
IOPS volume is provisioned with 4,000 IOPS (4,000 16KB reads or writes), for a total of 16,000
random IOPS on the instance. The EC2 instance initially delivers the expected 16,000 IOPS
random read and write performance. Sometime later, in order to increase the total random I/O
performance of the instance, you add an additional two 500 GB EBS Provisioned IOPS volumes
to the RAID. Each volume is provisioned to 4,000 IOPs like the original four, for a total of 24,000
IOPS on the EC2 instance. Monitoring shows that the EC2 instance CPU utilization increased
from 50% to 70%, but the total random IOPS measured at the instance level does not increase at
all.
What is the problem and a valid solution?

A.
The EBS-Optimized throughput limits the total IOPS that can be utilized; use an EBS-Optimized
instance that provides larger throughput.

B.
Small block sizes cause performance degradation, limiting the I/O throughput; configure the
instance device driver and filesystem to use 64KB blocks to increase throughput.

C.
The standard EBS Instance root volume limits the total IOPS rate; change the instance root
volume to also be a 500GB 4,000 Provisioned IOPS volume.

D.
Larger storage volumes support higher Provisioned IOPS rates; increase the provisioned volume
storage of each of the 6 EBS volumes to 1TB.

E.
RAID 0 only scales linearly to about 4 devices; use RAID 0 with 4 EBS Provisioned IOPS
volumes, but increase each Provisioned IOPS EBS volume to 6,000 IOPS.