Dell PERC 4/SI - Manual (Page 73)

The RAID controller controls hard drives via 320M SCSI buses (channels) over which the system transfers data in either LVD or 320M SCSI modes. Each
adapter controls two SCSI channels.
SCSI Disk Status
A SCSI disk drive (physical drive) can be in one of these four states:
l Online: A powered-on and operational disk.
l Hot Spare: A powered-on, stand-by disk ready for use if another disk fails.
l Not Responding: The disk is not present, not powered-on, or has failed.
l Rebuild: A disk to which one or more logical drives is restoring data.
SCSI ID
Each SCSI device on the RAID controller SCSI bus must have a different SCSI address number (Target ID or TID) from 0 to 15. Notice that one ID is used by the
SCSI controller, usually ID 7. Set the SCSI ID switch on each disk drive to the correct SCSI address. See the RAID controller documentation, chassis labels or
disk enclosure documentation for the correct switch settings.
Spare
A hard drive available to back up the data of other drives.
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.
Stripe Size
The amount of data written to each disk. Also called "stripe depth." You can specify stripe sizes of 2 KB, 4 KB, 8 KB, 16 KB, 32 KB, 64 KB, and 128 KB for each
logical drive. A larger stripe size produces improved read performance, especially if most of the reads are sequential. For mostly random reads, select a smaller
stripe size.
Stripe Width
The number of disk drives across which the data are striped.
Terminator
A resistor connected to a signal wire in a bus or network for impedance matching to prevent reflections, e.g., a resistor connected across signal wires at the
end of a SCSI cable.
Wide SCSI
A variant on the SCSI-2 interface. Wide SCSI uses a 16-bit bus, double the width of the original SCSI-1.
Write-Back
In Write-Back caching mode, the controller sends a data transfer completion signal to the host when the controller cache has received all the data in a disk
write transaction. Data are written to the disk subsystem in accordance with policies set up by the controller. These policies include the amount of dirty/clean
cache lines, the number of cache lines available, elapsed time from the last cache flush, and others.
Write-Through
In Write Through caching mode, the controller sends a data transfer completion signal to the host when the disk subsystem has received all the data in a
transaction. The controller cache is not used.
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