AWS EC2 Instance Comparison: C5d Vs C5n

Amazon’s compute-intensive C5 instance family has multiple instance types which can make it difficult to choose the right instance type for your use-case.

In this post, we will look at the differences between the C5, C5d and C5n instance types.

C5 instance family

Amazon added the C5d instance type at the beginning of 2018. These instances are equipped with local NVMe storage which improves disk performance greatly. Any application which relies on disk I/O performance would benefit from this instance type.

The C5n instance type was announced during latter part of 2018. The C5n instance type builds upon the C5d instance type and includes a lot of performance improvements especially increased network bandwidth.

Let’s take a closer look at the differences between these instance types.

Specs

The specs for these instance types are listed below:

Instance Type	Memory	vCPUs	Network Performance	Instance Store
c5d.large	4 GIB	2 vCPUs	Up to 10 Gbps	1 x 50 NVMe SSD
c5d.xlarge	8 GIB	4 vCPUs	Up to 10 Gbps	1 x 100 NVMe SSD
c5d.2xlarge	16 GIB	8 vCPUs	Up to 10 Gbps	1 x 200 NVMe SSD
c5d.4xlarge	32 GIB	16 vCPUs	Up to 10 Gbps	1 x 400 NVMe SSD
c5d.9xlarge	72 GIB	36 vCPUs	10 Gigabit	1 x 900 NVMe SSD
c5d.18xlarge	144 GIB	72 vCPUs	25 Gigabit	2 x 900 NVMe SSD

Instance Type	Memory	vCPUs	Network Performance
c5n.large	4 GIB	2 vCPUs	Up to 25 Gbps
c5n.xlarge	8 GIB	4 vCPUs	Up to 25 Gbps
c5n.2xlarge	16 GIB	8 vCPUs	Up to 25 Gbps
c5n.4xlarge	32 GIB	16 vCPUs	Up to 25 Gbps
c5n.9xlarge	72 GIB	36 vCPUs	50 Gigabit
c5n.18xlarge	144 GIB	72 vCPUs	100 Gigabit

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CPU Performance

We used Geekbench to compare the CPU performance of the two instance families. Geekbench is a processor benchmarking program. It runs a series of tests on a processor and times how long the processor takes to complete the tasks. The faster the CPU, the higher the score.

C5n instances are (slightly) faster than the C5d instances.

Instance Type	c5d score	c5n score	Improvement
xlarge	4166	4471	7%

Network Performance

We used iperf to compare the network performance of the two instance families. iperf measures maximum achievable bandwidth.

As expected, C5n instances have a much higher network bandwidth available to them.

C5d (c5d.xlarge)

[ ID] Interval Transfer Bandwidth [ 4] 0.0-60.0 sec 7.75 GBytes 1.11 Gbits/sec [ 7] 0.0-60.0 sec 7.75 GBytes 1.11 Gbits/sec [ 6] 0.0-60.0 sec 23.6 GBytes 3.39 Gbits/sec [ 14] 0.0-60.0 sec 3.63 GBytes 519 Mbits/sec [ 5] 0.0-60.0 sec 3.72 GBytes 532 Mbits/sec [ 9] 0.0-60.0 sec 4.84 GBytes 693 Mbits/sec [ 10] 0.0-60.0 sec 4.67 GBytes 668 Mbits/sec [ 11] 0.0-60.0 sec 3.88 GBytes 555 Mbits/sec [ 8] 0.0-60.0 sec 2.52 GBytes 361 Mbits/sec [ 13] 0.0-60.0 sec 7.75 GBytes 1.11 Gbits/sec [SUM] 0.0-60.0 sec 70.1 GBytes 10.0 Gbits/sec

C5n (c5n.xlarge)

[ ID] Interval Transfer Bandwidth [ 4] 0.0-60.0 sec 11.4 GBytes 1.63 Gbits/sec [ 9] 0.0-60.0 sec 11.4 GBytes 1.63 Gbits/sec [ 7] 0.0-60.0 sec 11.4 GBytes 1.63 Gbits/sec [ 11] 0.0-60.0 sec 22.4 GBytes 3.21 Gbits/sec [ 13] 0.0-60.0 sec 21.8 GBytes 3.12 Gbits/sec [ 5] 0.0-60.0 sec 21.8 GBytes 3.11 Gbits/sec [ 6] 0.0-60.0 sec 22.3 GBytes 3.20 Gbits/sec [ 8] 0.0-60.0 sec 21.8 GBytes 3.13 Gbits/sec [ 10] 0.0-60.0 sec 11.4 GBytes 1.63 Gbits/sec [ 15] 0.0-60.0 sec 21.8 GBytes 3.12 Gbits/sec [SUM] 0.0-60.0 sec 178 GBytes 25.4 Gbits/sec

Disk I/O Performance

We ran the following tests to measure the Disk I/O performance of the two instance types:

• dd: Comparing write performance
• hdparm: Test reading and caching performance

We did not see any noticeable difference in the disk I/O performance between the two instance types.

C5d (c5d.xlarge)

dd if=/dev/zero of=/tmp/test1.img bs=1G count=1 oflag=dsync 1+0 records in 1+0 records out 1073741824 bytes (1.1 GB) copied, 7.88091 s, 136 MB/s dd if=/dev/zero of=/tmp/test2.img bs=512 count=1000 oflag=dsync 1000+0 records in 1000+0 records out 512000 bytes (512 kB) copied, 1.34207 s, 382 kB/s sudo hdparm -Tt /dev/nvme0n1 /dev/nvme0n1: Timing cached reads: 18662 MB in 1.99 seconds = 9367.78 MB/sec Timing buffered disk reads: 514 MB in 3.01 seconds = 170.61 MB/sec

C5n (c5n.xlarge)

dd if=/dev/zero of=/tmp/test1.img bs=1G count=1 oflag=dsync 1+0 records in 1+0 records out 1073741824 bytes (1.1 GB) copied, 7.74249 s, 139 MB/s [ec2-user@ip-172-31-40-114 ~]$ [ec2-user@ip-172-31-40-114 ~]$ dd if=/dev/zero of=/tmp/test2.img bs=512 count=1000 oflag=dsync 1000+0 records in 1000+0 records out 512000 bytes (512 kB) copied, 1.43256 s, 357 kB/s sudo hdparm -Tt /dev/nvme0n1 /dev/nvme0n1: Timing cached reads: 16862 MB in 1.99 seconds = 8460.83 MB/sec Timing buffered disk reads: 514 MB in 3.01 seconds = 170.48 MB/sec

Pricing

C5n instances are approximately 8-12% more expensive than C5d instances.

Instance Type	c5d	c5n
xlarge	$0.192	$0.216

Conclusion

Overall, the C5n instances offer better performance (compute + network) than C5d instances. However, they are also more expensive than C5d instances. The choice for which instance type should depend on what the use-case is. If you need the extra network bandwidth, then it makes sense to go with the C5n instances otherwise the C5d or C5 instances might be a better choice.