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I created an AMI for my micro instance where I was running my application and launched a m1.medium with that image. This is a windows 2008 server class machine. I see that the instance has 3.7 GB of RAM as per the doc http://aws.amazon.com/ec2/instance-types/. But I found that it still has 1 CPU instead of 2 and 30GB hard disk, instead of 410GB. What's wrong ? In the aws console, the type is m1.medium though. I suspect my image would have created this problem. How can I rectify this ?

2 Answers 2

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I moved from micro to medium, but do not see any visible performance difference.

Remember, micro can burst up to the same level of CPU power as a medium instance. It just doesn't get to stay there very long. If you're not generating persistent loads, you may not notice a performance difference (other than the RAM difference).

Once you hit the micro CPU cap, it becomes pretty apparent.

30GB hard disk, instead of 410GB

You get 410GB of instance storage, but it's not mounted by default. You need to specifically tell the Amazon tools you'd like the instance storage mounted. From this tutorial: http://wishfulcode.com/2010/02/02/amazon-ec2-ephemeral-storage-on-ebs-backed-instances/

ec2-run-instances ami-4bebc03f -k myinstancekey -g my-security-group -b "xvdg=ephemeral0" -t c1.medium --availability-zone eu-west-1a

The -b "xvdg=ephemeral0" indicates that you'd like to mount one of the ephemeral drives.

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  • Thanks for clearing that up. Based on that article and what I know of EC2 it seems that using the extra ephemeral storage they provide is probably not a good idea. For the cost of the EBS drives it seems best just to stick with the EBS drives. At least know it makes sense why they put the numbers in their documentation.
    – bwight
    Mar 23, 2012 at 15:20
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    The ephemeral storage can be useful for storing temporary files, OS swapping, etc. Saves money and you don't mind if it all disappears.
    – ceejayoz
    Mar 23, 2012 at 16:15
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According to the Amazon Documentation http://aws.amazon.com/ec2/#instance

Medium Instance 3.75 GB of memory, 2 EC2 Compute Units (1 virtual core with 2 EC2 Compute Units each), 410 GB of local instance storage, 32-bit or 64-bit platform

You can see the part where they say 1 virtual core. This means that there is only 1 core. The 2 ECU is how powerful the machine is in amazon's rating. In this instance because the machine only has 1 core that means that the core is 2 ECU. If there were 2 cores and 2ECU then each core would only have the power of 1ECU. Again, referencing amazons documentation an ECU is:

EC2 Compute Unit (ECU) – One EC2 Compute Unit (ECU) provides the equivalent CPU capacity of a 1.0-1.2 GHz 2007 Opteron or 2007 Xeon processor.

Now as far as the harddrive goes... I Can't explain that. They always say the instance will have X amount of diskspace and for windows machines you'll always get 30GB for the root device and 8GB for linux.

If you need more than 30GB just add another EBS drive of the size you desire. Its really not a good idea to store application data on the root device anyways.

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  • Thank you Bwight. CPU thing is clear now. About hard disk, I see in the console, in elastic block store, that the capacity of the volume is 30GiB. There are options of "create volume" and "create snapshot" and "Change auto enable IO setting". Are you referring to create volume ?
    – user644745
    Mar 23, 2012 at 14:43
  • Also, I am using mongodb and redis and using the same instance for everything. Which means, mongo, redis and application everything run on medium instance in EC2. Is that fine ? I moved from micro to medium, but do not see any visible performance difference. Whereas when I run everything in my machine, I get a stunning performance. Is it because of the IO latency ?
    – user644745
    Mar 23, 2012 at 14:49
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    The auto enable IO setting is new. I just saw that yesterday not sure what it is. Yes i'm referring to create volume. Create snapshot is like creating a backup of a volume you already have data on. If you're application does not have high cpu requirements a medium machine should be fine. I recommend not using micro instances for production servers, see this article from amazon. docs.amazonwebservices.com/AWSEC2/latest/UserGuide/…
    – bwight
    Mar 23, 2012 at 15:16

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