[ubuntu-cloud] root volume of cluster compute instance

Scott Moser smoser at ubuntu.com
Wed Jun 1 16:44:28 UTC 2011

On Tue, 31 May 2011, Jonathan Marston wrote:

> Hello,
> I just fired up an ubuntu 11.04 cluster compute instance ( ebs-hvm-cluster, ami-1cad5275 )
> It looks great, fires up fine, but the root partition is only 10gb. Here is what df -h returns
> Filesystem            Size  Used Avail Use% Mounted on
> /dev/sda1             7.9G  2.5G  5.1G  33% /
> none                   12G  140K   12G   1% /dev
> none                   12G   88K   12G   1% /dev/shm
> none                   12G   96K   12G   1% /var/run
> none                   12G     0   12G   0% /var/lock
> The cc1.4xlarge is supposed to have 1690gb of space available to it which I would like to make available. T

It seems to me, that this is a bug on amazon's side.  When we register
images (with code at [1]), we do so with '--block-device-mapping' flags,
so that a single ephemeral device will be present by default.

It looks like that does not work for hvm instance types.  Unless there is
a bug that I'm not seeing in the code there, we' *are* invoking
ec2-register for hvm types with:
  --block-device-mapping /dev/sdb=ephemeral0
  --block-device-mapping /dev/sdc=ephemeral1

I just tested, and, using
  us-east-1 ami-1cad5275 hvm/ubuntu-natty-11.04-amd64-server-20110426

and different arguments for block-device-mapping to ec2-run-instances:
- fails: <no block-device-mapping args>
- works:
  --block-device-mapping sdb=ephemeral0 --block-device-mapping sdc=ephemeral1
- works:
  --block-device-mapping /dev/sdb=ephemeral0 --block-device-mapping /dev/sdc=ephemeral1

So, in short, use one of the above 2 block-device-mapping arguments if you
want ephemeral storage to be seen.

When I launch instances with ec2-run-instances, I use the code snippit at [2]
to get the right block-device-mapping flags.  See [3] for more info

[1] http://bazaar.launchpad.net/~ubuntu-on-ec2/ubuntu-on-ec2/ec2-publishing-scripts/view/head:/ec2-image2ebs
[2] https://gist.github.com/809587
[3] http://ubuntu-smoser.blogspot.com/2011/02/getting-ephemeral-devices-on-ebs-images.html

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