Donald K. Burleson Oracle RAC Tips

Multiple RAID Controllers and Storage Processors

RAID Controllers are the units in a storage array that control the RAID operations. They present one or more virtual devices (or LUNS) to the host system and distribute the I/O operations to the member disks. With the help of a RAID utility, the physical disks are grouped and formed into LUNS (logical units). The LUN is the basic storage unit presented to the host system for its use.

It is also responsible for maintaining the mapping between the virtual device and individual disks in the array. The existence of a RAID controller makes a JBOD array into a RAID Storage Array. RAID Controllers are also used in parallel access arrays for improving the I/O performance. Any failure in the RAID controller cripples the total functionality of the storage array.

Many of the storage arrays offer intelligent storage processors, which control the RAID activity on the array. The storage processor is the RAID controller for the storage array. In many arrays, there is a local cache to handle the data movement along with storage processors. Dual caches or battery-backed caches help with protection and provide additional redundancy. (See Fig 5.4)

Fig 5.4 Redundant RAID controllers