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For example, a system using a five-disk-drive RAID set can add another disk drive to create a six-disk-drive RAID set. The M.O.R.E. operation can be performed on all RAID levels except JBOD. Mylex’s Global Array Manager (GAM) supports two M.O.R.E. features: Expand Capacity allows logical drive expansion for FFx external controllers only. Expand Array allows array expansion for both PCI and FFx external controllers. During the RAID set expansion process, which includes re-striping data from the old (smaller) RAID set to the new (expanded) RAID set, the controller continues to service host I/O requests. MTBF Mean Time Between Failures, the average time from start of use to failure in a large population of identical systems, computers, or devices. Narrow SCSI 8-bit wide standard SCSI. Compare with Fast SCSI, Fast/Wide SCSI, Ultra SCSI, Ultra Wide SCSI, Ultra Fast SCSI, Ultra 160 SCSI, and WideSCSI. NVRAM Non-Volatile Random Access Memory, a memory unit equipped with a battery so that the data stays intact even after the main power had been switched off. AcceleRAID 170 Installation Guide Glossary Offline A Logical Drive is in an “offline” state if no data can be read from it or written to it. Offline does not apply to physical disk drives. System commands issued to offline logical drives are returned with an error status; no operations can be performed on offline logical drives. See also Logical Drive States, Online, and Critical. Online A Logical Drive is in an “online” state if all of its participating SCSI drives have power and are operational. See also Logical Drive States, Critical, and Offline. Parity A method of providing complete data redundancy while requiring only a fraction of the storage capacity of mirroring. The data and parity blocks are divided between the disk drives in such a way that if any single disk drive is removed or fails, the data on it can be reconstructed using the data on the remaining disk drives. The parity data may exist on only one disk drive or be distributed between all disk drives in a RAID group. Parity Check A function used to verify the integrity of data on a system drive. It verifies that mirror or parity information matches the stored data on the redundant arrays. If the parity block information is inconsistent with the data blocks, the controller corrects the inconsistencies. See also Consistency Check. PCI Peripheral Component Interconnect, a standardized architecture that provides a high-speed data path between peripherals and the CPU. PCI is a high-performance, backplane interface, expansion slot architecture found on PCs, Macintoshes, and UNIX workstations. PCI cards are portable across hardware platforms with the help of various software drivers. PCI Hot Plug A feature that allows for the printed circuit board (PCB) to be replaced without powering down the entire system—an essential feature in newer PCI-based PCs. Mylex DAC960PG, DAC960PJ, AcceleRAID, and eXtremeRAID products are all PCI Hot Plug compatible. See also Hot Plug. Manual No. 775064 G-13 Physical Device Any device connected to some kind of hardware. For example, SCSI disk, fibre disk, network disk, RAM disk, etc. Physical Disk Drive A single hard disk drive. Each physical disk drive is assigned a unique identification address. PROM Programmable Read-Only Memory, memory that users with appropriate instructions can reprogram. Protocol A special set of rules for transmitting data between two devices in a telecommunication connection. RAID Redundant Array of Independent Disks, a collection of two or more disks working together in an array. DAC960 controllers implement this technology to connect up to 15 SCSI devices per channel. The different forms of RAID implementation are known as “RAID levels.” The system manager or integrator selects the appropriate RAID level for a system. This decision will be based on which of the following are to be emphasized: Disk Capacity Data Availability (redundancy or fault tolerance) Disk Performance RAID Adapters See RAID Controller. RAID Advisory Board (RAB) An association of companies whose primary intention is to standardize RAID storage systems. Mylex is a member of RAB. RAID Controller Low cost RAID controllers that use SCSI channels on the motherboard. AcceleRAID 170 Installation Guide Glossary RAID Levels Mylex disk array controllers support four RAID Advisory Board approved (RAID 0, RAID 1, RAID 3, and RAID 5), two special (RAID 0+1, and JBOD), and three spanned (RAID 10, 30, and 50) RAID levels. All DAC960, AcceleRAID, and eXtremeRAID series controllers support these RAID levels. Level 0: Provides block “striping” across multiple drives, yielding higher performance than is possible with individual drives. This level does not provide any redundancy. Level 1: Drives are paired and mirrored. All data is 100 percent duplicated on a drive of equivalent size. Level 3: Data is “striped” across several physical drives. Maintains parity information, which can be used for da...