To cover all aspects of Oracle VM storage we must discuss both the provisioning and the consumption side of the storage functionality. The following sections provide an answer to two major questions:
How does Oracle VM connect to its storage?
What storage elements are available within the Oracle VM environment?
Oracle VM connects to its storage via Oracle Storage Connect plug-ins. Storage Connect plug-ins are packaged and distributed as RPM packages and deployed on the Oracle VM Servers. They are divided in two major categories: storage array plug-ins for any block based storage, and file system plug-ins for any network file system based storage.
For both categories, generic plug-ins are included. They offer standard functionality to discover, register and use NFS storage, iSCSI or Fibre Channel SANs, and local storage For more information about the types of storage supported in Oracle VM, see Section 4.2, “Storage Types”. The standard operations allowed via generic plug-ins are "passive", in the sense that they can detect and use storage elements offered to the Oracle VM Servers. Interactive management operations on the storage hardware is not possible with generic plug-ins.
In addition, Oracle cooperates with storage partners and invites storage hardware vendors to develop Oracle Storage Connect plug-ins for their specific hardware. These vendor-specific plug-ins can only be used with a specific brand or product line of storage hardware but they offer additional operations from within Oracle VM Manager compared to generic plug-ins. For example, a generic storage array plug-in can only detect LUNs on the storage host and has only a single access group to define which servers can access the storage elements. In contrast, a vendor-specific storage array plug-in allows interactive operations such as creating and modifying LUNs, and can configure various access groups for finer-grained storage access management. For detailed information about Oracle Storage Connect plug-ins, see Section 4.3, “Storage Connect Plug-ins”.
The main benefits of the plug-in approach are:
Flexibility. Use and integrate with your existing storage infrastructure, choose between file-based and block-based solutions, and use local storage for testing purposes or virtual machines of minor importance. Use generic or vendor-specific plug-ins depending on your available hardware or any new hardware you select.
Scalability. Add more storage providers of your preferred type and present them to your server pools as your need for storage increases. Reduce the amount of storage again if the higher storage requirements are temporary. Provision your storage with redundancy and multipathing according to your requirements and preferences.
Extensibility. If you upgrade your storage, consider the added functionality of vendor-specific plug-ins. If you select hardware for which Oracle Storage Connect plug-ins are available, ask the manufacturer for the RPM and install the plug-in on the Oracle VM Servers with access to this storage hardware.
Oracle VM always requires a location to store environment resources that are essential to the creation and management of virtual machines. These resources include VM templates and assemblies, ISO files (virtual DVD images), VM configuration files and VM virtual disks. The location of such a group of resources is called a storage repository. You present a storage repository to the Oracle VM Servers that need access to those resources; typically all servers in a server pool.
Storage repositories can be configured on an NFS file system or on a physical disk (LUN) of a storage array. However, for storage repositories on physical disk, the servers with access to it must be members of a clustered server pool. For unclustered server pools only file server storage is available. For details about the use of storage repositories, see Section 4.8, “Managing Storage Repositories”.
Clustering adds another storage element to the environment: the server pool file system. During server pool creation, the server pool file system specified for the new server pool is accessed and formatted as an OCFS2 file system, whether the file system is accessed by the Oracle VM Servers as an NFS share, a FC LUN or iSCSI LUN. This formatting creates several management areas on the file system including a region for the global disk heartbeat. The server pool file system plays a key role in clustering and therefore in the high-availability configuration of the Oracle VM environment. For details about server pool clustering, see Section 6.2, “Server Pool Clusters”.
The storage element that is most tangible and visible to all users of Oracle VM is the virtual machine disk. A VM disk is either a disk image file in a storage repository or a raw physical disk. If a physical disk (LUN) is used, it is attached directly to the VM in the same way it would be to a physical machine. For details about virtual machine operation, see Chapter 7, Managing Virtual Machines. Again, the availability of VM disks in a storage location with shared access from all Oracle VM Servers in the server pool is essential for VM high-availability.