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I just attached another ebs volume to running instance. But how do I access the volume? I can't find the /dev/sda directory anywhere. Where should I look?

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up vote 12 down vote accepted

When you attach an EBS volume, you specify the device to attach it as. Under linux, these devices are /dev/xvd* - and are symlinked to /dev/sd*

In the AWS console, you can see your EBS volumes, what instances they are attached to, and the device each volume is attached as:

AWS Console

You can achieve the same thing from the CLI tools. Set the necessary environment variables:

export EC2_PRIVATE_KEY=/root/pk-XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.pem 
export EC2_CERT=/root/cert-XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX.pem

Run the command on your current instance (otherwise, just specify the instance-id):

ec2-describe-instances `curl -s http://169.254.169.254/latest/meta-data/instance-id` | grep BLOCKDEVICE

BLOCKDEVICE     /dev/sda1       vol-xxxxxxxx    2011-11-13T21:09:53.000Z
BLOCKDEVICE     /dev/sdf        vol-xxxxxxxx    2011-11-13T21:09:53.000Z
BLOCKDEVICE     /dev/sdg        vol-xxxxxxxx    2011-11-13T21:09:53.000Z

It is worth noting that in both cases above - the CLI and the AWS Console - the devices are described as being attached at /dev/sd* - this is not actually the case, however.

Look at the contents of /dev:

ls -l /dev/sd* /dev/xv*
lrwxrwxrwx 1 root root       5 Dec 12 18:32 /dev/sda1 -> xvda1
lrwxrwxrwx 1 root root       4 Dec 12 18:32 /dev/sdf -> xvdf
lrwxrwxrwx 1 root root       4 Dec 12 18:32 /dev/sdg -> xvdg
brw-rw---- 1 root disk 202,  1 Dec 12 18:32 /dev/xvda1
brw-rw---- 1 root disk 202, 80 Dec 12 18:32 /dev/xvdf
brw-rw---- 1 root disk 202, 96 Dec 12 18:32 /dev/xvdg

The devices are actually /dev/xvd* - and the /dev/sd* paths are symlinks.

Another approach to check for the currently available devices is to use fdisk -l, or for a simpler output:

cat /proc/partitions
major minor  #blocks  name

 202        1    4194304 xvda1
 202       80    6291456 xvdf
 202       96    1048576 xvdg

If you need to determine which devices have been mounted use mount and df - and check /etc/fstab to change the mount options.

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Saved my butt. They really need to update those docs. –  MBHNYC Dec 16 '13 at 19:54
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