Appendix C GlossaryA proprietary enclosure management interface. It is intended to be used to warn RAID managers of enclosure environment component failures.Fault Bus -
Fibre - (Also known as "fibre channel.") A device (in the case of RAID, a data storage device) protocol capable of high data transfer rates. Fibre channel simplifies data bus sharing and supports not only greater speed, but also more devices on the same bus. Fibre channel can be used over both copper wire and optical cable.
Fiber - An optical network data transmission cable type which is unrelated to fibre channel (above).
HBA - Host-Bus Adapter an HBA is a device that permits a PC bus to pass data to and receive data from a storage bus (such as SCSI or fibre channel).
Host - A computer, typically a server, which uses a RAID system (internal or external) for data storage.
Host LUN - (See Host and LUN). "Host LUN" is another term for a LUN.
I2C a type of bus designed by Philips Semiconductors which is used to connect integrated circuits. I2C is a multi-master bus, which means that multiple chips can be connected to the same bus and each one can act as a master by initiating a data transfer.
In-Band SCSI - (sometimes "in-band" or "In-band") A means whereby RAID management software can use SCSI cabling and protocols to manage a controller.
ISEMS - Infortrend Simple Enclosure Management System an I2C-based enclosure monitoring standard developed by Infortrend Technologies, Inc.
JBOD - Just a Bunch of Drives non-RAID use of multiple hard disks for data storage.
JRE - Java Runtime Environment the Solaris Java program used to run .JAR applications locally or over a network or the internet.
Logical Drive - Typically, a group of hard disks logically combined to form a single large storage unit. More broadly, the assignment of a SCSI or Fibre channel ID to a drive or drives for use in storage management. Often abbreviated, "LD."
Logical Volume - A group of logical drives logically combined to form a single large storage unit. Often abbreviated, "LV."
LUN - Logical Unit Number A 3-bit identifier used on a SCSI bus to distinguish between up to eight devices (logical units) with the same SCSI ID.
Mapping - The assignment of a protocol or logical ID to a device for purposes of data storage, data transfer, or device management.
Mirroring - A form of RAID where two or more identical copies of data are kept on separate disks. Used in RAID 1.
NAS - Network Attached Storage a RAID enclosure that includes a network interface so that the disk array can be directly connected to a LAN.
NPC - Notification Processing Center a software application included with RAIDWatch which permits event notification via various methods including e-mail and fax.
NRAID - No RAID
Parity - Parity checking is used to detect errors in binary-coded data. The fact that all numbers have parity is commonly used in data communications to ensure the validity of data. This is called parity checking.
Primary Agent - The RAIDWatch module which manages secondary agents and supports both NPC and RAIDWatch Manager.
RAID - Redundant Arrays of Independent Disks (Originally "Redundant Arrays of Inexpensive Disks"). The use of two or more disk drives instead of one disk, which provides better disk performance, error recovery, and fault tolerance, and includes interleaved storage techniques and mirroring of important data. See Appendix D.
RAIDWatch Manager - The GUI RAID interface part of RAIDWatch.
SAF-TE - SCSI Accessed Fault-Tolerant Enclosures an evolving enclosure monitoring device type used as a simple real-time check on the go/no-go status of enclosure UPS, fans, and other items.
SAN - Storage Area Network is a high-speed subnetwork of shared storage devices. A storage device is a machine that contains nothing but a disk or disks for storing data. A SAN's architecture works in a way that makes all storage devices available to all servers on a LAN or WAN. Because stored data does not reside directly on the networks servers, server power is utilized for applications rather than for data passing.
SCSI - Small Computer Systems Interface (pronounced "scuzzy") a high-speed interface for mass storage that can connect computer devices such as hard drives, CD-ROM drives, floppy drives, and tape drives. SCSI can connect up to eight devices.
Secondary Agent - The RAIDWatch module which manages and monitors a RAID controller and receives RAIDWatch Manager commands via the primary agent.
S.M.A.R.T. - Self-Monitoring, Analysis and Reporting Technology an open standard for developing disk drives and software systems that automatically monitor a disk drive's health and report potential problems. Ideally, this should allow users to take proactive actions to prevent impending disk crashes.
Spare - (Local / Global) A drive designation used in RAID systems for drives that are not used but are instead "hot-ready" and used to automatically replace a failed drive. RAIDs generally support two types of spare, Local and Global. Local spares only replace drives that fail in the same logical drive. Global spares replace any drive in the RAID that fails.
Stripe - A contiguous region of disk space. Stripes may be as small as one sector or may be composed of many contiguous sectors.
Striping - Also called RAID-0. A method of distributing data evenly across all drives in an array by concatenating interleaved stripes from each drive.
Stripe Size - (A.k.a., "chunk size.") The smallest block of data read from or written to a physical drive. Modern hardware implementations let users to tune this block to the typical access patterns of the most common system applications.
Stripe Width - The number of physical drives used for a stripe. As a rule, the wider the stripe, the better the performance.
Write-back Cache - Many modern disk controllers have several megabytes of cache on board. Onboard cache gives the controller greater freedom in scheduling reads and writes to disks attached to the controller. In write-back mode, the controller reports a write operation as complete as soon as the data is in the cache. This sequence improves write performance at the expense of reliability. Power failures or system crashes can result in lost data in the cache, possibly corrupting the file system.
Write-through Cache - The opposite of write-back. When running in a write-through mode, the controller will not report a write as complete until it is written to the disk drives. This sequence reduces read/write performance by forcing the controller to suspend an operation while it satisfies the write request.