The large 850 GB drive space advertised with the instance information is "instance storage". That means that it's the drive space available on the physical hardware of the machine that you are running on.
When you create a new EC2 instance, if your instance is EBS-backed, then by default, this "instance storage" is not available to you. The 8 GB that you are seeing is the default 8 GB EBS volume created for your Linux instance.
To access your desired 100 GB, you have 2 options:
- Increase the size of your root EBS volume to 100 GB during the launch wizard. Use 'resize2fs' to access the full volume size after initial boot.
- Map the "instance storage" to a device during the launch wizard. You'll need to mount and create your file system on this volume after initial boot.
Alternatively, you can create an "instance-backed" EC2 instance instead of an EBS-backed instance. This will put your root volume on the "instance storage" of the hardware. Beware though that "instance-backed" instances cannot be stopped and you'll lose all data if the instance is terminated.