Glossary
Keywords: MegaRAID SAS SW UG

> Glossary

> This appendix provides a glossary for terms used in this document.

> | C |
> Cache |  | Fast memory that holds recently accessed data. Use of cache memory speeds subsequent access to the same data. When data is read from or written to main memory, a copy is also saved in cache memory with the associated main memory address. The cache memory software monitors the addresses of subsequent reads to see if the required data is already stored in cache memory. If it is already in cache memory (a cache hit), it is read from cache memory immediately and the main memory read is aborted (or not started). If the data is not cached (a cache miss), it is fetched from main memory and saved in cache memory.
> CC |  | CacheCade.
> Caching |  | The process of using a high speed memory buffer to speed up a computer system’s overall read/write performance. The cache can be accessed at a higher speed than a drive subsystem. To improve read performance, the cache usually contains the most recently accessed data, as well as data from adjacent drive sectors. To improve write performance, the cache can temporarily store data in accordance with its write back policies.
> CLI |  | Command Line Interface.
> Coercion |  | A controller property indicating the capacity to which drives of nominally identical capacity are coerced (forced) to make them usable in a storage configuration.
> Controller |  | A chip that controls the transfer of data between the microprocessor and memory or between the microprocessor and a peripheral device such as a drive. RAID controllers perform RAID functions such as striping and mirroring to provide data protection.
> | D |
> DAS |  | Direct Attached Storage.
> Device ID |  | A controller or drive property indicating the manufacturer-assigned device ID.
> Device port count |  | A controller property indicating the number of ports on the controller.
> Drive cache policy |  | A virtual drive property indicating whether the virtual drive cache is enabled, disabled, or unchanged from its previous setting.
> Drive group |  | A group of drives attached to a RAID controller on which one or more virtual drives can be created. All virtual drives in the drive group use all of the drives in the drive group.
> Drive state |  | A drive property indicating the status of the drive. A drive can be in one of the following states:
> | Online – A drive that can be accessed by the controller and is a part of the virtual drive.
> | Offline – A drive that is part of a virtual drive, but which has invalid data as far as the controller configuration is concerned.
> | Ready for Online – When a cached logical drive is plugged back to be brought online, the ready for online message.
> Drive type |  | A drive property indicating the characteristics of the drive.
> | G |
> GPL |  | General Public Licensing.
> GUI |  | Graphical User Interface.
> | H |
> HDD |  | Hard Disk Drive.
> KVM |  | Kernel-based Virtual Machine.
> | M |
> Multipathing |  | The firmware provides support for detecting and using multiple paths from the controllers to the SAS devices that are in enclosures. Devices connected to enclosures have multiple paths to them. With redundant paths to the same port of a device, if one path fails, another path can be used to communicate between the controller and the device. Using multiple paths with load balancing, instead of a single path, can increase reliability through redundancy.
> | O |
> Offline |  | A drive is offline when it is part of a virtual drive but its data is not accessible to the virtual drive.
> OS |  | Operating System.
> | P |
> Product name |  | A controller property indicating the manufacturing name of the controller.
> | R |
> RPM |  | Redhat Package Manager.
> | S |
> SAN |  | Storage Area Network.
> SAS |  | Acronym for Serial-Attached SCSI. SAS is a serial, point-to-point, enterprise-level device interface that leverages the Small Computer System Interface (SCSI) protocol set. The SAS interface provides improved performance, simplified cabling, smaller connectors, lower pin count, and lower-power requirements when compared to parallel SCSI.
> SATA |  | Acronym for Serial Advanced Technology Attachment. A physical storage interface standard. SATA is a serial link that provides point-to-point connections between devices. The thinner serial cables allow for better airflow within the system and permit smaller chassis designs.
> SCSI device type |  | A drive property indicating the type of the device, such as drive.
> Serial no. |  | A controller property indicating the manufacturer-assigned serial number.
> SSD |  | Solid State Drive.
> | V |
> Virtual drive |  | A storage unit created by a controller chip from one or more drives. Although a virtual drive (logical drive) can be created from several drives, it is seen by the operating system as a single drive. Depending on the RAID level used, the virtual drive can retain redundant data in case of a drive failure.
> VMM |  | Virtual Machine Management.
> VT |  | Virtualization Technology.
> | W |
> WD |  | LSI SSD Module, a PCI device: WarpDrive.
> | X |
> XD |  | Accelerate Disk.

DB15-000917-02-January 2013
Copyright© 2013 by LSI Corporation. All rights reserved.