Working with the AutoEnableIO Volume Attribute on EC2 volumes.

It’s a setting not likely to be accessed often, but it’s good to be a aware of the AutoEnableIO Volume Attribute on EC2 volumes in AWS.

In the EC2 Dashboard, you’ll find it under Volumes > Select Volume > Actions >Change Auto Enable IO Setting.

autoenableIO1.png     autoenableIO3.png

So what does this setting do?

“When Amazon EBS determines that a volume’s data is potentially inconsistent, it disables I/O to the volume…” [1]

However, if you check the box to Auto-Enable Volume IO, it will override the setting, enabling IO to the affected volume.

When you provision a new instance, Auto-Enable Volume IO is enabled on the root volume by default.

When you provision a new, non-root volume, this is NOT enabled.

Let’s say you’re working with an EC2 instance and one of its non-root volumes status check shows ‘impaired’ status.  (This would be returned when one of AWS’s automatic volume status checks give a Fail response).

You could try and force IO to the volume by enabling this feature. However, keep in mind, that this would mean that you’re working on a potentially inconsistent volume. Depending on the data on the volume, this could be a reasonable action.

At the very least, it’s good to know a bit about how this works in the event that you have an impaired EC2 volume.

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