Dell PERC 4/DC User Manual
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SCSI
(small computer system interface) A processor-independent standard for system-level interfacing between a system and intelligent devices, including hard
disks, diskettes, CD drives, printers, scanners, etc. SCSI can connect up to seven devices to a single adapter (or host adapter) on the system's bus. SCSI
transfers eight or 16 bits in parallel and can operate in either asynchronous or synchronous modes. The synchronous transfer rate is up to 320 MB/sec. SCSI
connections normally use single-ended drivers, as opposed to differential drivers.
The original standard is now called SCSI-1 to distinguish it from SCSI-2 and SCSI-3, which include specifications of Wide SCSI (a 16-bit bus) and Fast SCSI (10
MB/sec transfer.) Ultra 160M SCSI is a subset of Ultra3 SCSI and allows a maximum throughput of 160 MB/sec, which is more than twice as fast as Wide Ultra2
SCSI. Ultra320 SCSI allows a maximum throughput of 320 MB/sec.
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. Logical drives
can span consecutively numbered arrays that each consist of the same number of hard drives. Array spanning promotes RAID level 1 to RAID levels 10. See
also
Array Spanning
, and
Disk Spanning
.
Spare
A hard drive available to back up the data of other drives.
Stripe Size
The amount of data contiguously written to each disk. You can specify stripe sizes of 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, and 128 KB for each logical drive. For
best performance, choose a stripe size equal to or smaller than the block size used by the host system.
Stripe Width
The number of hard drives across which the data are striped.
Striping
Segmentation of logically sequential data, such as a single file, so that segments can be written to multiple physical devices in a round-robin fashion. This
technique is useful if the processor can read or write data faster than a single disk can supply or accept it. While data is being transferred from the first disk,
the second disk can locate the next segment. Data striping is used in some modern databases and in certain RAID devices.
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