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2.15. Hypervisor Support for Primary Storage

The following table shows storage options and parameters for different hypervisors.
VMware vSphere
Citrix XenServer
KVM
Oracle VM
Format for Disks, Templates, and Snapshots
VMDK
VHD
QCOW2
RAW
iSCSI support
VMFS
Clustered LVM
Yes, via Shared Mountpoint
Yes, via OCFS2M
Fiber Channel support
VMFS
Yes, via Existing SR
Yes, via Shared Mountpoint
No
NFS support
Y
Y
Y
Y
Local storage support
Y
Y
Y
Y
Storage over-provisioning
NFS and iSCSI
NFS
NFS
No
XenServer uses a clustered LVM system to store VM images on iSCSI and Fiber Channel volumes and does not support over-provisioning in the hypervisor. The storage server itself, however, can support thin-provisioning. As a result the CloudStack can still support storage over-provisioning by running on thin-provisioned storage volumes.
KVM supports "Shared Mountpoint" storage. A shared mountpoint is a file system path local to each server in a given cluster. The path must be the same across all Hosts in the cluster, for example /mnt/primary1. This shared mountpoint is assumed to be a clustered filesystem such as OCFS2. In this case the CloudStack does not attempt to mount or unmount the storage as is done with NFS. The CloudStack requires that the administrator insure that the storage is available
Oracle VM supports both iSCSI and NFS storage. When iSCSI is used with OVM, the CloudStack administrator is responsible for setting up iSCSI on the host, including re-mounting the storage after the host recovers from a failure such as a network outage. With other hypervisors, CloudStack takes care of mounting the iSCSI target on the host whenever it discovers a connection with an iSCSI server and unmounting the target when it discovers the connection is down.
With NFS storage, CloudStack manages the overprovisioning. In this case the global configuration parameter storage.overprovisioning.factor controls the degree of overprovisioning. This is independent of hypervisor type.
Local storage is an option for primary storage for vSphere, XenServer, Oracle VM, and KVM. When the local disk option is enabled, a local disk storage pool is automatically created on each host. To use local storage for the System Virtual Machines (such as the Virtual Router), set system.vm.use.local.storage to true in global configuration.
CloudStack supports multiple primary storage pools in a Cluster. For example, you could provision 2 NFS servers in primary storage. Or you could provision 1 iSCSI LUN initially and then add a second iSCSI LUN when the first approaches capacity.