Why volume stuck in the "Attaching" state？

Question

I created an EC2 instance with a d3.8xlarge instance type. According to the AWS documentation ( https://docs.aws.amazon.com/zh_cn/AWSEC2/latest/UserGuide/volume_limits.html#instance-type-volume-limits ), this instance type only supports mounting three volumes. However, I mounted four volumes A, B, C, and D. While A,B,C mounted successfully, the fourth volume D has been stuck in the "Attaching" state. If I detach one of the mounted volumes (A, B, or C), then volume D will mount successfully. I am wondering why AWS designed it this way. The documentation clearly states that the d3.8xlarge instance type only supports three volumes. So, why doesn't AWS throw an error when attempting to mount the fourth volume, instead of keeping it stuck in "Attaching" state? Is there a specific reason behind this design?

Answer

Check that the device name you specified when you attempted to attach the EBS volume isn't already in use. If the specified device name is already being used by the block device driver of the EC2 instance, the operation fails.

If you specify a device name that's not in use by Amazon EC2, but is used by the block device driver within the EC2 instance, the attachment of the Amazon EBS volume fails. Instead, the EBS volume is stuck in the attaching state. To know more about the reasons, Kindly refer the below Knowledge Centre article.

[+] https://repost.aws/knowledge-center/ebs-stuck-attaching

Why volume stuck in the "Attaching" state？

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