[two types of storage]
The cinder-volume service which provide persistent block storage vs. the ephemeral storage provided by the instance flavor.
- Ephemeral
Rebooting the VM or restarting the host server will not destroy ephemeral data. data will be deleted if the instance is terminated;
In the typical use case an instance's root filesystem is stored on ephemeral storage.
In addition to the ephemeral root volume all flavors except the smallest, m1.tiny, provide an additional ephemeral block device varying from 20G for the m1.small through 160G for the m1.xlarge by default.
This is presented as a raw block device with no partition table or filesystem. Cloud aware operating system images may discover, format, and mount this device. For example the cloud-init package included in Ubuntu's stock cloud images will format this space as an ext3 filesystem and mount it on /mnt.
- Persistent (Volume)
Volume storage is independent of any particular instance and is persistent. Volumes are user created and within quota and availability limits may be of any arbitrary size.
When first created volumes are raw block devices with no partition table and no filesystem. They must be attached to an instance to be partitioned and/or formatted. Once this is done they may be used much like an external disk drive.
It is possible to configure a volume so that it is bootable and provides a persistent virtual instance similar to traditional non-cloud based virtualization systems. In this use case the resulting instance may still have ephemeral storage depending on the flavor selected, but the root filesystem (and possibly others) will be on the persistent volume and thus state will be maintained even if the instance it shutdown.
Volumes do not provide concurrent access from multiple instances. For that you need either a traditional network filesystem like NFS or CIFS or a cluster filesystem such as GlusterFS.
The cinder-volume service which provide persistent block storage vs. the ephemeral storage provided by the instance flavor.
- Ephemeral
Rebooting the VM or restarting the host server will not destroy ephemeral data. data will be deleted if the instance is terminated;
In the typical use case an instance's root filesystem is stored on ephemeral storage.
In addition to the ephemeral root volume all flavors except the smallest, m1.tiny, provide an additional ephemeral block device varying from 20G for the m1.small through 160G for the m1.xlarge by default.
This is presented as a raw block device with no partition table or filesystem. Cloud aware operating system images may discover, format, and mount this device. For example the cloud-init package included in Ubuntu's stock cloud images will format this space as an ext3 filesystem and mount it on /mnt.
- Persistent (Volume)
Volume storage is independent of any particular instance and is persistent. Volumes are user created and within quota and availability limits may be of any arbitrary size.
When first created volumes are raw block devices with no partition table and no filesystem. They must be attached to an instance to be partitioned and/or formatted. Once this is done they may be used much like an external disk drive.
It is possible to configure a volume so that it is bootable and provides a persistent virtual instance similar to traditional non-cloud based virtualization systems. In this use case the resulting instance may still have ephemeral storage depending on the flavor selected, but the root filesystem (and possibly others) will be on the persistent volume and thus state will be maintained even if the instance it shutdown.
Volumes do not provide concurrent access from multiple instances. For that you need either a traditional network filesystem like NFS or CIFS or a cluster filesystem such as GlusterFS.
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