Some Pouta virtual machine flavors have an ephemeral storage in addition to the root disk. This works as additional storage for the duration of the instance. This storage is not saved with the instance. This storage does not get saved when you create a snapshot of an image. It is not copied along with resizes or migrations. It is especially important to note regarding the io.* flavors that the storage is based on RAID0 arrays optimized for performance, providing no redundancy whatsoever.
For a detailed explanation of the ephemeral storage (and other storage options), you can see the storage concepts section in the OpenStack user guide.
The ephemeral storage is visible as an additional disk to the virtual machine (usually /dev/vdb). You need to format and mount it before you can use it:
sudo mkfs.ext4 /dev/vdb sudo mount /dev/vdb /mnt
You also need to add an entry in the /etc/fstab file on the machine to make sure the disk gets mounted after a reboot:
sudo umount /mnt/ sudo e2label /dev/vdb EPHEMERAL sudo echo "LABEL=EPHEMERAL /mnt ext4 defaults,nofail 0 2 " >> /etc/fstab sudo mount /mnt
Some legacy flavors (tiny, mini, small, medium, large, fullnode) also contained an ephemeral disk which was preformatted and mounted automatically.