4.1 Ephemeral storage

Some Pouta virtual machine flavors have ephemeral storage in addition to a 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 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 will need to format and mount it first before you can use it:

sudo mkfs.ext4 /dev/vdb
sudo mount /dev/vdb /mnt

You will also need to add an entry to 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.

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