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I launched an EBS backed AMI with all the defaults.

I noticed that it automicatlly had attached an ephemeral disk.

I was just wondering if there was a good programtic way to know that this particular device is ephemeral vs some EBS volume I had decided to attach:

ubuntu@-----:~$ df -ahT
Filesystem     Type        Size  Used Avail Use% Mounted on
/dev/xvda1     ext4        7.9G  867M  6.7G  12% /
proc           proc           0     0     0    - /proc
sysfs          sysfs          0     0     0    - /sys
none           fusectl        0     0     0    - /sys/fs/fuse/connections
none           debugfs        0     0     0    - /sys/kernel/debug
none           securityfs     0     0     0    - /sys/kernel/security
udev           devtmpfs    1.9G   12K  1.9G   1% /dev
devpts         devpts         0     0     0    - /dev/pts
tmpfs          tmpfs       751M  172K  750M   1% /run
none           tmpfs       5.0M     0  5.0M   0% /run/lock
none           tmpfs       1.9G     0  1.9G   0% /run/shm
/dev/xvdb      ext3        394G  199M  374G   1% /mnt

ubuntu@-----:~$ mount
/dev/xvda1 on / type ext4 (rw)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
udev on /dev type devtmpfs (rw,mode=0755)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
tmpfs on /run type tmpfs (rw,noexec,nosuid,size=10%,mode=0755)
none on /run/lock type tmpfs (rw,noexec,nosuid,nodev,size=5242880)
none on /run/shm type tmpfs (rw,nosuid,nodev)
/dev/xvdb on /mnt type ext3 (rw,_netdev)
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1 Answer 1

up vote 1 down vote accepted

If you're talking in-VM programatic way, not really; your best bet is to know they show up, where they mount, and plan accordingly.

That said, with the EC2 API you can determine what's supposed to be there. The ec2-describe-instance call will give you a list of block-device mappings. So long as you're playing with the API, you can create instances with the block-device mappings you want.

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