Local storage consists of hard disks installed locally in your Oracle VM Server. In a default installation, Oracle VM Server will only use the first disk (/dev/sda), leaving other disks available for storage.

As long as no partition and data are present the device will be detected as a raw disk. The choice is yours to use the local disks either to provision logical storage volumes as disks for virtual machines or to install a storage repository. If you place a storage repository on the local disk, an OCFS2 file system is installed. If you intend to create a storage repository on a local disk, the disk must not contain any data or meta-data. In this case, it is necessary to clean the disk manually before attempting to create a storage repository on it. This can be used by using the dd command:

# dd if=/dev/zero of=/dev/disk bs=1M

Where disk is the device name of the disk where you wish to create the repository. Note that this action is destructive and that data on the device where you perform this action may be rendered irretrievable. Also note that the installation process does not clean disks that are not specified for the actual installation. Therefore, if you have installed Oracle VM Server on a system that contains other disks with pre-existing data, you may choose to clean these disks manually for use as local storage repositories.

Local storage is fairly easy to set up because no special hardware for the disk subsystem is required. Since the virtualization overhead in this setup is limited, and disk access is internal within one physical server, local storage offers reasonably high performance.

However, the downsides are quickly revealed when you think about configurations with multiple Oracle VM Servers. Local storage by definition remains local and cannot be shared between different servers. Therefore, even if you set up a pool of multiple servers and use the advantages of clustering, virtual machines using local storage can never benefit from high availability: they cannot be migrated from one server to another.

Network Attached Storage – typically NFS – is a commonly used file-based storage system that is very suitable for the installation of Oracle VM storage repositories. Storage repositories contain various categories of resources such as templates, virtual disk images, DVD ISO files and virtual machine configuration files, which are all stored as files in the directory structure on the remotely located, attached file system. Since most of these resources are rarely written to but are read frequently, NFS is ideal for storing these types of resources.

With Oracle VM you discover NFS storage via the server IP or host name and typically present storage to all the servers in a server pool to allow them to share the same resources. This, along with clustering, helps to enable high availability of your environment: virtual machines can be easily migrated between host servers for the purpose of load balancing or protecting important virtual machines from going off-line due to hardware failure.

NFS storage is exposed to Oracle VM Servers in the form of shares on the NFS server which are mounted onto the Oracle VM Server's file system. Since mounting an NFS share can be done on any server in the network segment to which NFS is exposed, it is possible not only to share NFS storage between servers of the same pool but also across different server pools.

In terms of performance, NFS is slower for virtual disk I/O compared to a logical volume or a raw disk. This is due mostly to its file-based nature. For better disk performance you should consider using block-based storage, which is supported in Oracle VM in the form of iSCSI or Fibre Channel SANs.

With Internet SCSI, or iSCSI, you can connect storage entities to client machines, making the disks behave as if they are locally attached disks. iSCSI enables this connectivity by transferring SCSI commands over existing IP networks between what is called an initiator (the client) and a target (the storage provider).

To establish a link with iSCSI SANs, all Oracle VM Servers can use configured network interfaces as iSCSI initiators. It is the user's responsibility to:

Performance-wise an iSCSI SAN is better than file-based storage like NFS and it is often comparable to direct local disk access. Because iSCSI storage is attached from a remote server it is perfectly suited for a clustered server pool configuration where high availability of storage and the possibility to live migrate virtual machines are important factors.

Provisioning of iSCSI storage can be done through open source target creation software at no additional cost, with dedicated high-end hardware or with anything in between. The generic iSCSI Storage Connect plug-in allows Oracle VM to use virtually all iSCSI storage providers. In addition, vendor-specific Storage Connect plug-ins exist for certain types of dedicated iSCSI storage hardware, allowing Oracle VM Manager to access additional interactive functionality otherwise only available through the management software of the storage provider. Examples are creating and deleting LUNs, extending existing LUNs and so on. Check with your storage hardware supplier if a Storage Connect plug-in is available. For installation and usage instructions, consult your supplier's plug-in documentation.

Functionally, a fibre channel SAN is hardly different from an iSCSI SAN. Fibre channel is actually older technology and uses dedicated hardware instead: special controllers on the SAN hardware, host bus adapters or HBAs on the client machines, and special fibre channel cables and switches to interconnect the components.

Like iSCSI, a Fibre Channel SAN transfers SCSI commands between initiators and targets establishing a connectivity that is almost identical to direct disk access. However, whereas iSCSI uses TCP/IP, a Fibre Channel SAN uses Fibre Channel Protocol (FCP). The same concepts from the iSCSI SAN, as described above, apply equally to the Fibre Channel SAN. Again, generic and vendor-specific Storage Connect plug-ins exist. Your storage hardware supplier will provide proper documentation with the Storage Connect plug-in.