Dell PERC 4/DC - Manual (Page 89)

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Glossary
Dell™ PowerEdge™ Expandable RAID Controller 4/SC, 4/DC, and 4e/DC User's Guide
A • C • D • F • G • H • I • L • M • O • P • R • S
Array
A grouping of hard drives that combines the storage space on the hard drives into a single segment of contiguous storage space. The RAID controller can
group hard drives on one or more channels into an array. A hot spare drive does not participate in an array.
Array Spanning
Array spanning by a logical drive combines storage space in two arrays of hard drives into a single, contiguous storage space in a logical drive. The logical
drive can span consecutively numbered arrays, each having the same number of hard drives. Array spanning promotes RAID level 1 to RAID level 10. See also
Disk Spanning , and Spanning .
Asynchronous Operations
Operations that are not related to each other in time and can overlap. The concept of asynchronous I/O operations is central to independent access arrays in
throughput-intensive applications.
Cache I/O
A small amount of fast memory that holds recently accessed data. Caching speeds subsequent access to the same data. It is most often applied to processor-
memory access, but can also be used to store a copy of data accessible over a network. 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.
Channel
An electrical path for the transfer of data and control information between a disk and a disk controller.
Clearing
In the BIOS Configuration Utility, the option used to delete information from physical drives.
Consistency Check
An examination of the data in the hard drives in a logical drive to ensure that the data is redundant.
Cold Swap
A cold swap requires that you power down the system before replacing a defective hard drive in a disk subsystem.
Data Transfer Capacity
The amount of data per unit time moved through a channel. For disk I/O, bandwidth is expressed in megabytes per second (MB/sec).
Degraded Drive
A logical drive that has become non-functional or has a hard drive that is non-functional.
Disk
A non-volatile, randomly addressable, rewritable mass storage device, including both rotating magnetic and optical disks and solid-state disks, or non-volatile
electronic storage elements. It does not include specialized devices such as write-once-read-many (WORM) optical disks, nor does it include so-called RAM
disks implemented using software to control a dedicated portion of a host system's volatile random access memory.
Disk Array
A collection of disks from one or more disk subsystems combined using a configuration utility. The utility controls the disks and presents them to the array
operating environment as one or more logical drives.
Disk Mirroring
Disk mirroring is the process of duplicating the data onto another drive (RAID 1) or set of drives (in RAID 10), so that if a drive fails, the other drive has the
same data and no data is lost.
Disk Spanning
Disk spanning allows multiple logical drives to function as one big logical drive. Spanning overcomes lack of disk space and simplifies storage management by
combining existing resources or adding relatively inexpensive resources. See also
Array Spanning and Spanning .
Disk Striping
A type of disk array mapping. Consecutive stripes of data are mapped round-robin to consecutive array members. A striped array (RAID level 0) provides high
I/O performance at low cost, but provides no data redundancy.