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when I boot the ubuntu 10.04 EBS image from alestic on EC2 I get two drives. /dev/sda1 seems like the root device and it's on 15GB. I find it in my volume folder in the AWS.

I also get an 150GB partition called /dev/sda2, but I don't really understand what this is. Also, it doesn't seem to persist between stops of the instance.

So, my question is, what is this /dev/sda2 partition and how should I relate to it?

Also, is there some good documentation explaining and describing persistent instances on EC2? I find it really confusing to understand volum, aim, snapshot, ebs, s3 and so on. Thanks!

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The /dev/sda2 partition is the standard temporary storage that all EC2 instances provide; as you noticed, this is non-persistent storage that goes away when you stop the instance. On UNIX instances it's usually mounted as /mnt - you can use it if you need large amounts of temporary storage for log files that you don't need to keep, or for storing the temporary files needed wehen you create a custom AMI from your instance.

Have a look at the AWS docs on EBS backed instances if you want to have an instance where all the file systems are persistent.

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  • So when I have the esb backed instance in "stopped" mode, the volum is automatically stored on S3? I also wonder, if I want a smaller volume attached than the 15GB volume from alestic, I guess that can be attached using the APIs? Thanks for your reply. I need to spend some more time to work on this and your help is very appreciated. – grm Jul 9 '10 at 5:53
  • EBS volumes are a separate technology to S3 - just think of them as persistent volumes of a fixed size with built-in redundancy (Amazon says they are 4 times more reliable than physical hard drives). So with your EBS-backed instance, the root volume will be preserved between instance stop and start just as if it was on a physical drive. You certainly can switch out your EBS volume for a smaller one; just check out the EBS documentation. No problem on the help, just holler if you need more ! – gareth_bowles Jul 9 '10 at 15:48

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