The SAN Volume Controller is a SAN appliance that attaches open-systems storage devices to supported open-systems hosts. The IBM TotalStorage SAN Volume Controller provides symmetric virtualization by creating a pool of managed disks from the attached storage subsystems, which are then mapped to a set of virtual disks for use by attached host computer systems. System administrators can view and access a common pool of storage on the SAN, which enables them to use storage resources more efficiently and provides a common base for advanced functions.
The SAN Volume Controller is analogous to a logical volume manager (LVM) on a SAN. It performs the following functions for the SAN storage that it is controlling:
A node is a single storage engine. The storage engines are always installed in pairs with one or two pairs of nodes constituting a cluster. Each node in a pair is configured to back up the other. Each pair of nodes is known as an I/O group. All I/O operations handled by the nodes in an I/O group are cached on both nodes for resilience. Each virtual volume is defined to an I/O group. To eliminate any single point of failure, each of the two nodes in the I/O group are protected by different uninterruptible power supplies.
The SAN Volume Controller I/O groups see the storage presented to the SAN by the back-end controllers as a number of disks, known as managed disks. The application services do not see these managed disks. Instead, they see a number of logical disks, known as virtual disks, that are presented to the SAN by the SAN Volume Controller. Each node must only be in one I/O group and provide access to the virtual disks in the I/O group.
The SAN Volume Controller helps to provide continuous operations and can also optimize the data path to ensure performance levels are maintained.
The fabric contains two distinct zones: a host zone and a disk zone. In the host zone, the host systems can identify and address the nodes. You can have more than one host zone. Generally, you will create one host zone per operating system type. In the disk zone, the nodes can identify the disk drives. Host systems cannot operate on the disk drives directly; all data transfer occurs through the nodes. As shown in Figure 2, several host systems can be connected to a SAN fabric. A cluster of SAN Volume Controllers is connected to the same fabric and presents virtual disks to the host systems. You configure these virtual disks using the disks located on the RAID controllers.
![]() | Note: You can have more than one host zone. Generally, you create one host zone per operating system type, because some operating systems will not tolerate other operating systems in the same zone. |
When hardware service or maintenance is required, you can remove one node in each I/O group from a cluster. After you remove the node, you can replace the field replaceable units (FRUs) in the node. All disk drive communication and communication between nodes is performed through the SAN. All SAN Volume Controller configuration and service commands are sent to the cluster through an Ethernet network.
Each node contains its own vital product data (VPD). Each cluster contains vital product data that is common to all the nodes on the cluster. Any system connected to the Ethernet network can access this VPD.
Enclosure configuration information is stored on every node that is in the cluster to allow concurrent replacement of FRUs. An example of this information might be information that is displayed on the menu screen of the SAN Volume Controller. When a new FRU is installed, and when the node is added back into the cluster, configuration information that is required by that node is ready from other nodes in the cluster.
![]() | Note: The multipath drivers, SDD and RDAC, can coexist on a host for certain operating systems. |
Check the following Web site for the latest support and coexistence information:
The SAN Volume Controller provides the following user interfaces:
The SAN Volume Controller provides the following application programming interface: