The glossary lists acronyms and defines RAID terms found throughout the documentation. It also includes definitions of the operational states for disk drives and logical drives.
A pair of components, such as storage controllers in a failure-tolerant RAID array, that share a task or set of tasks when both are functioning normally. When one component of the pair fails, the other takes the entire load. Dual active controllers are connected to the same set of devices and provide a combination of higher I/O performance and greater failure tolerance than a single controller.
American National Standards Institute.
Address Resolution Protocol.
A process in which data is automatically reconstructed after a drive failure and written to a standby (spare) drive. An automatic rebuild also occurs when a new drive is installed manually in place of a failed drive. If the rebuild process is interrupted by a reset, use the Manual Rebuild command from the firmware application to restart the rebuilding process.
block striping with dedicated parity
(RAID 3) A technique that breaks data into logical blocks, the size of a disk block, and then stripes these blocks across several drives. One drive is dedicated to parity. In the event that a disk fails, the original data can be reconstructed using the parity information and the information on the remaining drives.
Allows data to be stored in a predesignated area of a disk or RAM (random access memory). Caching is used to speed up the operation of RAID arrays, disk drives, computers and servers, or other peripheral devices.
The total number of physical drives available for data storage in a RAID array (logical drive). For example, if the capacity is N-1 and the total number of disk drives in a logical drives is six 36-Mbyte drives, the disk space available for storage is equal to five disk drives (5 x 36-Mbyte or 180 Mbyte).
Any path used for the transfer of data and control information between storage devices and a storage controller or I/O adapter. Also refers to one SCSI bus on a disk array controller. Each disk array controller provides at least one channel.
International Special Committee on Radio Interference.
Dynamic Host Configuration Protocol.
See mirroring (RAID1).
Event monitoring unit.
Fibre Channel network built around one or more switches.
Functions as a routing engine that actively directs data transfer from source to destination and arbitrates every connection. Bandwidth per node via a Fabric switch remains constant when more nodes are added, and a node on a switch port uses a data path of up to 100 Mbyte/sec to send or receive data.
A mode of operation for failure-tolerant arrays in which a component has failed and its function has been assumed by a redundant component.
The capacity to cope with internal hardware problems without interrupting the array's data availability, often by using backup systems brought online when a failure is detected. Many arrays provide fault tolerance by using RAID architecture to give protection against loss of data when a single disk drive fails. Using RAID 1 (mirroring), RAID 3 or RAID 5 (striping with parity), or RAID 1+0 (mirroring and striping) techniques, the array controller can reconstruct data from a failed drive and write it to a standby or replacement drive.
fault-tolerant logical drive
A logical drive that provides protection of data in the event of a single drive failure by employing RAID 1, 1+0, 3, or 5.
(Fibre Channel-Arbitrated Loop) FC-AL is implemented as either a loop or a Fabric. A loop can contain up to 126 nodes, accessible through only one or two servers.
A cost-effective gigabit communications link deployed across a wide range of hardware.
Fibre Channel HBAs
Fibre channel adapters of a host computer, server, or workstation.
An Arbitrated Loop Hub is a wiring concentrator. "Arbitrated" means that all nodes communicating over this Fibre loop are sharing a 100 Mbyte/sec segment. Whenever more devices are added to a single segment, the bandwidth available to each node is further divided. A loop configuration allows different devices in the loop to be configured in a token ring style. With a Fibre hub, a Fibre loop can be rearranged in a star-like configuration because the hub itself contains port bypass circuitry that forms an internal loop. Bypass circuits can automatically reconfigure the loop once a device is removed or added without disrupting the physical connection to other devices.
(Gigabyte) 1024 Mbyte or 1,073,741,824 bytes
(Gigabit Interface Converter) A hot-swappable input/output device that plugs into a Gigabit Ethernet port or Fibre Channel.
A spare drive that is available to all logical drives in an array. Spare drives can be part of automatic logical drive rebuild.
A group is a data object that enables multiple servers to be contained under a single category. Groups are similar in concept to domains, and enable you to organize servers.
Host bus adapter.
A drive in a RAID 1 or RAID 5 configuration that contains no data and acts as a standby in case another drive fails.
The ability of a field-replaceable unit (FRU) to be removed and replaced while the RAID array remains powered on and operational.
The process of writing a specific pattern to all data blocks on all drives in a logical drive. This process overwrites and destroys existing data on the disks and the logical drive. Initialization is required to make the entire logical drive consistent at the onset. Initialization ensures that any parity checks performed in the future are executed correctly.
(Just a Bunch of Disks) A storage device that consist of drives with no controllers.
Local area network.
A section of disk storage space that is presented to the host operating system as a single physical drive. A logical drive might be located on one or more physical drives.
(Logical Unit Number) The major and minor device numbers make up the logical unit numbering sequence for a particular device connected to a computer.
The ability to change the virtual LUN as presented to the server from storage. This enables such benefits as the ability of a server to boot from the SAN without requiring a local disk drive.
The characteristic that enables an administrator to dynamically map an HBA to a specified LUN. This provides an individual server or multiple servers access to an individual drive or to multiple drives, and prohibits unwanted server access to the same drives.
(Low-Voltage Differential) A low-noise, low-power, and low-amplitude signaling technology that enables data communication between a supported server and storage devices. LVD signaling uses two wires to drive one signal over copper wire and requires a cable that is no longer than 25 meters (82 ft.).
The 10/100BASE-T Ethernet port that is used to configure a RAID array.
(Megabyte) 1024 Kbyte or 1,048,576 bytes
A background process that continuously checks physical drives for bad blocks or other media errors.
mirroring (RAID 1)
Data written to one disk drive is simultaneously written to another disk drive. If one disk fails, the other disk can be used to run the array and reconstruct the failed disk. The primary advantage of disk mirroring is 100 percent data redundancy. Since the disk is mirrored, it does not matter if one of the disks fails. Both disks contain the same data at all times and either can act as the operational disk.
Disk mirroring provides 100 percent redundancy but is expensive because each drive in the array is duplicated.
multiple-block striping with distributed parity
A RAID technique (RAID 5) that offers redundancy with the parity information distributed across all disks in the logical drive. Data and its parity are never stored on the same disk. In the event that a disk fails, the original data can be reconstructed using the parity information and the information on the remaining disks.
Network Data Management Protocol.
(non-volatile random access memory) A memory unit equipped with a battery so that the data stays intact even after main power is switched off.
A Fibre Channel port in a point-to-point or Fabric connection.
OpenBoot PROM (OBP). When you first start Solaris, it shows an OK prompt, which is the OBP. It is a command-line interface.
Refers to the connections and devices that are not in the data path.
A process whereby the integrity of the redundant data on fault-tolerant arrays (RAID 3 and 5) is checked. The parity checking procedure on a logical drive recalculates the parity of data stripes in each of the logical drive's RAID stripe sets and compares it with the stored parity. If a discrepancy is found, an error is reported and the new correct parity is substituted for the stored parity. For RAID 1 configurations, data is compared with mirrored data, but since RAID 1 does not store parity, no automatic correction is possible.
A pair of interconnected controller units. Expansion units interconnected to the pair of controller units can also be part of the partner group.
Primary controller identifier number
(Programmable Logic Array) Offers flexible features for more complex designs.
(Programmable logic device) A generic term for an integrated circuit that can be programmed in a laboratory to perform complex functions.
(redundant array of independent disks) An arrangement of two or more disk drives combined into a single virtual drive to provide more disk storage space, better performance and reliability, and redundant backup of data. Various combinations of these features are described by defined RAID levels. Arrays can support RAID 0, 1, 1+0, 3, and 5.
Various techniques using combinations of mirroring, striping, duplexing, and parity to implement a RAID array are called RAID levels. Each technique uses a distinct algorithm to offer a mix of performance, reliability and cost.
Reverse Address Resolution Protocol.
(Reliability, Availability, and Serviceability) A variety of features and initiatives all designed to maximize equipment uptime and mean time between failures, minimize downtime and the length of time necessary to repair failures, and eliminate or decrease single points of failure in favor of redundancy.
A storage device parameter that determines whether the storage device holds data in cache before storing it to disk. The ability to hold data in cache while it is being written to disk can increase storage device speed during sequential reads.
The process of reconstructing the data that was on a disk before it failed. Rebuilding can be done only in arrays with data redundancy, such as RAID levels 1, 1+0, 3, and 5.
Enables the RAID controller to serve other I/O requests while rebuilding the logical drives. Priority ranges from low, which uses the controller's minimum resources to rebuild, to high, which uses the controller's maximum resources to complete the rebuilding process.
(Storage Area Network) A high-speed, open-standard, scalable network of storage devices and servers providing accelerated data access.
(Small Computer Systems Interface) An industry standard for connecting disk and tape devices to a workstation.
An interface to SCSI Enclosure Services devices. These devices sense and monitor physical conditions within an enclosure, and enable access to the status reporting and configuration features of the enclosure (such as indicator LEDs on the enclosure).
Secondary controller identifier number.
(Self-Monitoring Analysis and Reporting Technology) The industry-standard reliability prediction indicator for both the IDE/ATA and SCSI hard disk drives. Hard disk drives with SMART offer early warning of some hard disk failures so critical data can be protected.
(Simple Mail Transfer Protocol) A protocol for sending email messages between servers and from mail clients to mail servers. The messages can then be retrieved with an email client using either POP or IMAP.
(Simple Network Management Protocol) A set of protocols for managing complex networks. SNMP works by sending messages, called protocol data units (PDUs), to different parts of a network. SNMP-compliant devices, called agents, store data about themselves in Management Information Bases (MIBs) and return this data to the SNMP requesters.
Making use of the firmware's striping capability to stripe data across two otherwise independent RAID logical drives. The two spanned logical drives are presented to the operating system as one logical drive.
A drive that is marked as a spare to support automatic data rebuilding after a physical drive associated with a logical drive fails. For a standby drive to take the place of another drive, it must be at least equal in size to the failed drive and all of the logical drives dependent on the failed disk must be redundant--RAID 1, 1+0, 3, and 5.
The current operational status of a disk drive, a logical drive, or controller. The RAID array stores the states of drives, logical drives, and the controller in its nonvolatile memory. This information is retained across power interruptions.
The amount of data in kilobytes that is striped across each physical drive in a logical drive. Generally, large stripe sizes are more effective for arrays with sequential reads.
The storing of sequential blocks of incoming data on all the different physical drives in a logical drive.
This method of writing data increases the disk array throughput because multiple drives are working simultaneously, retrieving and storing. RAID 0, 1+0, 3, and 5 and all use striping.
A part used to end a SCSI bus. Terminators prevent energy from reflecting back into a cable plant by absorbing the radio frequency signals.
Uninterruptible Power Supply.
One or more drives that can be grouped into a unit for data storage.
A cache-writing strategy in which the array controller receives the data to be written to disk, stores it in the memory buffer, and immediately sends the host operating system a signal that the write operation is complete, without waiting until the data is actually written to the disk drive. Within a short time, the controller, when not busy, writes the data to the disk drive.
A cache-writing strategy used to control write operations. The write policy options are CIFS write-back and write-through cache.
A cache-writing strategy in which the array controller writes the data to the disk drive before signaling the host operating system that the process is complete. Write-through cache has lower write operation and throughput performance than write-back cache, but it is the safer strategy, with minimum risk of data loss on power failure.
(worldwide name) A globally unique, hard-coded and embedded number assigned by the manufacturer and registered under IEEE that is used to identify hardware.