A storage system, or storage controller, is a device that coordinates and controls the operation of one or more disk drives. A storage system synchronizes the operation of the drives with the operation of the system as a whole.
Storage systems provide the storage that a SAN Volume Controller cluster detects as one or more managed disks (MDisks).
SAN Volume Controller supports both RAID and non-RAID storage systems. RAID storage systems provide redundancy at the disk level, which prevents a single physical disk failure from causing an MDisk, MDisk group or associated VDisk failure. To minimize data loss, only virtualize the following RAID storage systems: RAID 1, RAID 10, RAID 0+1 and RAID 5.
Many storage systems can be used for storage that is provided by a RAID to be divided up into many Small Computer System Interface (SCSI) logical units (LUs) that are presented on the SAN. With the SAN Volume Controller, ensure that the storage systems are configured to present each RAID as a single SCSI LU that are recognized by the SAN Volume Controller as a single MDisk. The virtualization features of the SAN Volume Controller can then be used to divide up the storage into VDisks.
The exported storage devices are detected by the cluster and reported by the user interfaces. The cluster can also determine which MDisks each storage system is presenting and can provide a view of MDisks that is filtered by the storage system. Therefore, you can associate the MDisks with the RAID that the system exports.
The storage system can have a local name for the RAID or single disks that it is providing. However it is not possible for the nodes in the cluster to determine this name, because the namespace is local to the storage system. The storage system makes the storage devices visible with a unique ID, called the logical unit number (LUN). This ID, along with the storage system serial number or numbers (there can be more than one controller in a storage system), can be used to associate the MDisks in the cluster with the RAID exported by the system.
The size of an MDisk cannot be changed once it becomes a managed MDisk by adding it to an MDisk group. If the size of the LUN that is presented by the storage system is reduced to below the size of the managed MDisk, the MDisk is taken offline by the SAN Volume Controller. If the size of the LUN that is presented by the storage system is increased, the SAN Volume Controller does not use the additional space. To increase the storage capacity that is managed on a storage system, create a new LU on the storage system and add the MDisk that represents this LU to the MDisk group.