EC2实例DiskReadBytes与EBS卷VolumeReadBytes指标差异咨询

Hey there! I totally get this confusion—when I first started digging into AWS storage metrics, I mixed these up too. Let's break it down clearly:

First: What's the difference between a Disk and a Volume? #

• EBS Volume: This is a cloud-native block storage resource you create in AWS. It's a standalone, persistent storage unit (like gp3, io2, or st1) that you can attach to an EC2 instance. Think of it as the "raw storage bucket" AWS manages for you.
• Disk: This is what your EC2 instance's operating system sees. When you attach an EBS Volume to an instance, the OS recognizes it as a disk (e.g., /dev/xvda or /dev/sda1 on Linux). Also, some EC2 instances come with local instance storage (like NVMe SSDs on m5d/c5d instances)—the OS will also treat these as disks, even though they aren't EBS Volumes.

Now: Comparing EC2 DiskReadBytes vs EBS VolumeReadBytes #

Let's use your example metrics to highlight the key differences:

1. EC2 DiskReadBytes #

• Perspective: This metric comes from the EC2 instance's OS level.
• What it counts: Total bytes read from all disks recognized by the instance. That includes:
  • Any EBS Volumes attached to the instance
  • Local instance storage (if your instance type has it)
• Dimension: It's tracked per EC2 instance (you can filter by specific disk devices if needed).

2. EBS VolumeReadBytes #

• Perspective: This metric comes directly from the EBS service itself.
• What it counts: Only the bytes read from that specific EBS Volume. It doesn't care which instance the volume is attached to, and it completely ignores local instance storage.
• Dimension: It's tracked per individual EBS Volume.

Real-World Example #

• Scenario 1: You're using a t3.micro (no local storage) with one EBS gp3 volume attached. Here, DiskReadBytes and VolumeReadBytes will be nearly identical (minor discrepancies might come from OS-level caching, but the overall trend will match).
• Scenario 2: You're using a c5d.2xlarge (has local NVMe storage) and you're reading data from both the EBS volume and the local storage. Now, DiskReadBytes will be larger than the EBS volume's VolumeReadBytes—because it's adding up reads from both the EBS disk and the local disk.

内容的提问来源于stack exchange，提问作者Dhanraj