2.7. About Secondary Storage

2.7. About Secondary Storage

Secondary storage stores the following:

• Templates — OS images that can be used to boot VMs and can include additional configuration information, such as installed applications
• ISO images — disc images containing data or bootable media for operating systems
• Disk volume snapshots — saved copies of VM data which can be used for data recovery or to create new templates

The items in secondary storage are available to all hosts in the scope of the secondary storage, which may be defined as per zone or per region.

To make items in secondary storage available to all hosts throughout the cloud, you can add object storage in addition to the zone-based NFS Secondary Staging Store. It is not necessary to copy templates and snapshots from one zone to another, as would be required when using zone NFS alone. Everything is available everywhere.

CloudStack provides plugins that enable both OpenStack Object Storage (Swift,swift.openstack.org) and Amazon Simple Storage Service (S3) object storage. When using one of these storage plugins, you configure Swift or S3 storage for the entire CloudStack, then set up the NFS Secondary Staging Store for each zone. The NFS storage in each zone acts as a staging area through which all templates and other secondary storage data pass before being forwarded to Swift or S3. The backing object storage acts as a cloud-wide resource, making templates and other data available to any zone in the cloud.