Overland Storage SnapSAN S2000 User Manual page 237

SnapSAN S2000 User Guide
SAS
Short for Serial Attached SCSI. It is a point-to-point serial protocol that replaces
parallel SCSI bus technology (multidrop) and uses the standard SCSI command set. It
has no termination issues, supports up to 16,384 devices (using expanders), and
eliminates clock skew. It consists of an Initiator that originates device service
requests, a Target containing logical units that receives device service requests, and a
Service Delivery Subsystem that transmits information between the Initiator and the
Target.
SCSI
Short for Small Computer System Interface. SCSI is an industry standard for
connecting peripheral devices and their controllers to an initiator. Storage devices are
daisy-chained together and connected to a host adapter. The host adapter provides a
shared bus that attached peripherals use to pass data to and from the host system.
Examples of devices attached to the adapter include disk drives, CD-ROM discs,
optical disks, and tape drives. In theory, any SCSI device can be plugged into any
SCSI controller.
SCSI addressing
Each device supported by a SCSI adapter has its own unique SCSI address, which
dictates the device's priority when arbitrating for access to the SCSI bus. A SCSI
address of 7 has the highest priority. For a fast/wide SCSI adapter that supports up to
16 devices, the next highest priority address is 6, then 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11,
10, 9, and 8. The narrow SCSI adapter supports up to eight devices, including itself.
The SCSI address 7 has the highest priority, followed by 6, 5, 4, 3, 2, 1, and 0.
SCSI bus
A SCSI bus provides a means of transferring data between SCSI devices. A SCSI bus
is either an 8- or 16-bit bus that supports up to 8 or 16 devices, including itself. The
bus can consist of any mix of initiators and targets, with the requirement that at least
one initiator and one target must be present.
SCSI device
A SCSI device is a single unit on a SCSI bus that originates or services SCSI
commands. A SCSI device is identified by a unique SCSI address. SCSI devices can act
as initiators or targets.
SCSI port
A SCSI port is an opening at the back of a router that provides connection between the
SCSI adapter and SCSI bus.
Session
When an initiator wants to establish a connection with a target, it establishes what is
known as an iSCSI session. A session consists of one or more TCP/IP connections
between an initiator and a target. Sessions are normally established (or re-
established) automatically when the host computer starts up, although they also can
be established (and broken) manually.
SMS
Short for Short Message Service. Is a means of sending short text messages to a mobile
phone.
10400277-004 07/2011
©2010-11 Overland Storage, Inc.
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