Root Device on SSD instance types. SSD vs EBS confusion

Question

I have an AMI that was originally created from a t1.micro linux. The "Root Device Type" of this AMI is EBS (8 GB) and my web application software is "baked" into this root volume.

Now I would like to launch an m3.medium instance from this AMI but it has "Instance Storage" of 4GB SSD.

Will my newly launched m3.medium instance take advantage of the SSD storage at all? Or do I need to create a new AMI with "Instance Store" as the root "Root Device Type"?

Similarly ... When I try to launch an m3.medium from scratch using the "Amazon Linux AMI 2013.09.2" it adds an 8GB Root EBS volume by default that cannot be removed using the launch wizard.

What am I missing here?

Dupe of: http://serverfault.com/questions/583289/aws-ec2-migration-to-new-instance-type-with-ssd-drives — Chris Moschini, Jun 14 '14 at 20:09

score 6 · Answer 1 · answered Feb 01 '14 at 01:26

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Regardless of what it has as instance storage, it'll boot off an EBS drive. You can mount the SSD as an additional drive - this can be handy for swap space, temporary files, caches, etc.

answered Feb 01 '14 at 01:26

ceejayoz

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Hello ceejayoz, Thanks for the response. Yes that seems to be the case. After a little more research I discovered that when you launch an EC2 instance and select, for example, the m3.medium instance size, you may add additional storage on the "4. Add Storage" page of the launch wizard. On this page, you click on "Add New Volume" and then select "Instance Store 0" from the type drop-down box. For an m3.medium instance this will create a 4GB SSD based Instance Store volume for your instance. This volume will be accessible as /mnt on your instance. – user183744 Feb 05 '14 at 17:28
I'm trying to change my instance to a new type with 2x80GB SSDs. I already have a 100GB mounted EBS Volume and I was going to try to move those data files to the SSD files of the new instance. However, after changing instance type, I only have an 8GB mounted drive and a 15GB tempfs. I don't know where my 2 x 80G SSD drives are. – paiego Mar 20 '14 at 00:37
@paiego They're not mounted by default, you'll have to mount them. – ceejayoz Mar 20 '14 at 00:38

score 4 · Answer 2 · answered Jul 15 '14 at 06:08

Worth noting for future readers Amazon made 'general purpose' SSDs available across EBS. You can select then via the console, or via the apis as 'gp2'. They're a few cents a month more expensive than standard magnetic drives.

http://aws.amazon.com/blogs/aws/new-ssd-backed-elastic-block-storage/ http://aws.amazon.com/ebs/details/

score 0 · Answer 3 · answered Jul 15 '14 at 06:17

The SSD instance storage (as well as the magnetic instance storage) is ephemeral, and I don't believe it's guaranteed to persist if you do things like shut the instance down and then start it up again later (if it is migrated between hosts, for instance, the ephemeral volume doesn't stay with it).

It's really only useful for scratch space (caching, temp, etc.), for which it is very convenient and free, and doesn't consume bandwidth; EBS uses the instance's network bandwidth (except on EBS-optimized instances, where it uses a dedicated SAN interface).

Root Device on SSD instance types. SSD vs EBS confusion

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