Safe to Use an Amazon EBS Volume While Snapshot in Progress?

You're safe to use the volume once you have triggered the snapshot, even if it's still in a pending state according to AWS - see this post.

If you're taking a snapshot for the first time, it probably will take a while as it has to make a full copy to the region-wide S3 bucket, but remember, it's incremental after the first one has been stored so should be a lot faster.

NOTE: You can't create a volume out of a snapshot which is in a pending state. You'll get the error "Snapshot is in invalid state" if you do this.

So please make sure to wait until the snapshot is in the "available" state.

It's perfectly safe to use the volume during a snapshot. As soon as the snapshot command returns, the drive goes into a mode where new data is written elsewhere, so the snapshot is of what the drive looked like when you started.

However, you will experience very degraded performance (as you have noticed) until the snapshot is complete.

So make sure you only take your snapshots during off peak hours.