Object overview

Each SAN Volume Controller single processing unit is called a node. Nodes are deployed in pairs to make up a clustered system. A system can consist of one to four pairs of nodes. Each pair of nodes is known as an I/O group and each node can be in only one I/O group.

Volumes are logical disks that are presented by the systems. Each volume is associated with a particular I/O group. The nodes in the I/O group provide access to the volumes in the I/O group. When an application server performs I/O to a volume, it can access the volume with either of the nodes in the I/O group. Because each I/O group has only two nodes, the distributed cache is only two way.

Nodes that do not contain battery modules must be connected to an uninterruptible power supply, which provides data integrity if a system-wide power failure occurs. In such situations, the uninterruptible power supply maintains power to the nodes while the contents of the distributed cache are dumped to an internal drive.

The nodes in a system see the storage that is presented by back-end storage systems as a number of disks, which are known as managed disks (MDisks).

Each MDisk is divided into a number of extents, which are numbered from 0, sequentially from the start to the end of the MDisk.

MDisks are collected into groups, which are known as storage pools.

Each volume is made up of one or two volume copies. Each volume copy is an independent physical copy of the data that is stored on the volume. A volume with two copies is known as a mirrored volume. Volume copies are made out of MDisk extents. All the MDisks that contribute to a particular volume copy must belong to the same storage pool.

A volume can be thin-provisioned. This means that the virtual capacity of the volume, as seen by host systems, can be different from the amount of storage that is allocated to the volume from MDisks, called the real capacity. Thin-provisioned volumes can be configured to automatically expand their real capacity by allocating new extents.

At any one time, a single node in a system can manage configuration activity. This node is known as the configuration node and manages a cache of the information that describes the system configuration and provides a focal point for configuration.

For a SCSI over Fibre Channel (FC) or Fibre Channel over Ethernet (FCoE) connection, the nodes detect the FC or FCoE ports that are connected to the SAN. These ports correspond to the worldwide port names (WWPNs) of the FC or FCoE host bus adapters (HBAs) that are present in the application servers. You can create logical host objects that group WWPNs that belong to a single application server or to a set of them.

The system uses world wide port names (WWPNs) to identify the iSCSI, SAS, and Fibre Channel ports on the host server. The system uses the iSCSI qualified name (IQN) to identify iSCSI hosts.

For a SCSI over Ethernet connection, the iSCSI qualified name (IQN) identifies the iSCSI target (destination) adapter. Host objects can have both IQNs and WWPNs.

SAN Volume Controller hosts are virtual representations of the physical host systems and application servers that are authorized to access the system volumes. Each SAN Volume Controller host definition specifies the connection method, the port or IQN, and the volumes that the host applications can access.

The system provides block-level aggregation and volume management for disk storage within the SAN. The system manages a number of back-end storage systems and maps the physical storage within those storage systems into logical disk images that can be seen by application servers and workstations in the SAN. The SAN is configured in such a way that the application servers cannot see the back-end physical storage. This prevents any possible conflict between the system and the application servers both trying to manage the back-end storage.