Painlessly Increase Your EBS Based Root Volume Without Rebuilding

You created an AWS instance and decided to make a small root volume. Maybe you were shortsighted or just being cheap. Now the root volume is nearly full and you can’t expand it because you didn’t use LVM.

[ec2-user@ip-172-16-14-78 ~]$ df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/xvda1 8256952 8173060 8 100% /

To add insult to injury, AWS recently cut the price of EBS storage in half. This issue can be fixed with a handful of commands from the CLI.

Before you begin, take note of a few important details about the instance. You need to know the instance-id and the availability-zone that your instance is running in. You can get the instance-id from the running instance by querying the instance metadata service. More details about the metadata service are available here.

[ec2-user@ip-172-16-14-78 ~]$ curl http://169.254.169.254/latest/meta-data/instance-id/
i-2db6840d

Determine which availability-zone your instance is running in.

dcolon@dcolonbuntu:~$ aws ec2 describe-instances --instance-id i-2db6840d --output text | egrep ^PLACEMENT
PLACEMENT default None us-east-1a

Shut down the instance. You can’t get a reliable snapshot of a volume while it’s attached to a running instance.

dcolon@dcolonbuntu:~$ aws ec2 stop-instances --instance-ids i-2db6840d --output text
i-2db6840d
CURRENTSTATE 64 stopping
PREVIOUSSTATE 16 running
RESPONSEMETADATA e8b8f0ab-7cd1-478f-a7c1-bb5bf81b2355

To determine the volume-id of the root volume run describe-instances:

dcolon@dcolonbuntu:~$ aws ec2 describe-instances --instance-ids i-2db6840d --output text | egrep ^EBS
EBS attached True vol-b6b98bfb 2014-02-11T20:36:00.000Z

Take a snapshot of vol-b6b98bfb:

dcolon@dcolonbuntu:~$ aws ec2 create-snapshot --volume-id vol-b6b98bfb --output text
None vol-b6b98bfb pending 8 None 2014-02-11T21:10:41.000Z snap-e76a3b25 647956677678
RESPONSEMETADATA 03f83444-a473-4bc1-b138-1065f6d5cee0

Now that you have a snapshot (snap-e76a3b25) of the root volume, you can create an exact larger copy of it. If the snapshot state is still pending, you will get an error. Do not forget to specify the size or the new volume will be the same size as the old.

dcolon@dcolonbuntu:~$ aws ec2 create-volume --availability-zone us-east-1a --size 40 --snapshot-id snap-e76a3b25 --output text
us-east-1a standard vol-b4aa98f9 creating snap-e76a3b25 2014-02-11T21:14:51.280Z 40
RESPONSEMETADATA 2257dac5-1685-488c-b545-2f8f9417a6ac

Finally detach the original volume (vol-b6b98bfb) and attach the newly created volume (vol-b4aa98f9).

dcolon@dcolonbuntu:~$ aws ec2 detach-volume --volume-id vol-b6b98bfb --output text
2014-02-11T20:36:00.000Z i-2db6840d vol-b6b98bfb detaching /dev/sda1
RESPONSEMETADATA ea10cbbd-2adf-43c9-b5e3-cca19c1e5c26
dcolon@dcolonbuntu:~$ aws ec2 attach-volume --volume-id vol-b4aa98f9 --instance-id i-2db6840d --device /dev/sda1 --output text
2014-02-11T21:20:00.318Z i-2db6840d vol-b4aa98f9 attaching /dev/sda1
RESPONSEMETADATA 146b0ecc-6916-49aa-931c-24c6cdbaca8c

Start your instance and verify that your root volume is now 40 GB.

dcolon@dcolonbuntu:~$ aws ec2 start-instances --instance-id i-2db6840d --output text
i-2db6840d
CURRENTSTATE 0 pending
PREVIOUSSTATE 80 stopped
RESPONSEMETADATA 9320cb43-589f-4ab5-a1ce-d23718c02297
dcolon@dcolonbuntu:~$ ssh -i .ssh/prd.pem ec2-user@172.16.14.78
ssh: connect to host 172.16.14.78 port 22: Connection refused
dcolon@dcolonbuntu:~$ ssh ec2-user@172.16.14.78
Last login: Tue Feb 11 21:06:04 2014 from

__| __|_ )
_| ( / Amazon Linux AMI
___|\___|___|

[ec2-user@ip-172-16-14-78 ~]$ df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/xvda1 7.9G 7.8G 92M 99% /

The root volume is still 8 GB. This is because the volume was created based on a snapshot. Run resize2fs to resize the volume to 40 GB.

[ec2-user@ip-172-16-14-78 ~]$ sudo resize2fs /dev/xvda1
resize2fs 1.42.3 (14-May-2012)
Filesystem at /dev/xvda1 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 3
The filesystem on /dev/xvda1 is now 10485760 blocks long.
[ec2-user@ip-172-16-14-78 ~]$ df -h /
Filesystem Size Used Avail Use% Mounted on
/dev/xvda1 40G 7.8G 32G 20% /

For details on how to grow an EBS based LVM filesystem, see this article that I wrote.

If you have any questions, please post them in the comments below.