SAF-TE
Encyclopedia
In computer storage, a SCSI
Accessed Fault-Tolerant
Enclosure
is an industry standard to interface an enclosure to a (parallel
) SCSI subystem to gain access to information or control concerning
Practically, any given SAF-TE device will only support a subset of all possible sensors or controls.
Many RAID
controllers can utilize a SAF-TE 'activated' backplane
by detecting a swapped drive (after a defect) and automatically starting a rebuild. A passive subsystem usually requires a manual rescan and rebuild.
A SAF-TE device is represented as a SCSI processor device
that is polled every couple of seconds by e.g. the RAID controller software. Due to the low overhead required, impact on bus performance is negligible. For SAS
or Fibre Channel
systems, SAF-TE is replaced by the more standardized SCSI Enclosure Services
.
The most widely used version was defined in 'SAF-TE Interface Specification Intermediate Review R041497
April 14, 1997' by nStor (now Xyratex
) and Intel.
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
Accessed Fault-Tolerant
Fault-tolerant system
Fault-tolerance or graceful degradation is the property that enables a system to continue operating properly in the event of the failure of some of its components. A newer approach is progressive enhancement...
Enclosure
Disk enclosure
A disk enclosure is essentially a specialized chassis designed to hold and power disk drives while providing a mechanism to allow them to communicate to one or more separate computers. Drive enclosures provide power to the drives therein and convert the data sent across their native data bus into a...
is an industry standard to interface an enclosure to a (parallel
Parallel SCSI
Parallel SCSI is one of the interface implementations in the SCSI family. In addition to being a data bus, SPI is a parallel electrical bus: There is one set of electrical connections stretching from one end of the SCSI bus to the other. A SCSI device attaches to the bus but does not interrupt it...
) SCSI subystem to gain access to information or control concerning
- temperature
- fan status
- slot status (populated/empty)
- door status
- power supplies
- alarms
- indicators (e.g. LEDsLight-emitting diodeA light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
, LCDsLiquid crystal displayA liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....
)
Practically, any given SAF-TE device will only support a subset of all possible sensors or controls.
Many RAID
RAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
controllers can utilize a SAF-TE 'activated' backplane
Backplane
A backplane is a group of connectors connected in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors forming a computer bus. It is used as a backbone to connect several printed circuit boards together to make up a complete...
by detecting a swapped drive (after a defect) and automatically starting a rebuild. A passive subsystem usually requires a manual rescan and rebuild.
A SAF-TE device is represented as a SCSI processor device
SCSI Peripheral Device Type
A SCSI Peripheral Device Type is a way of describing what capabilities are provided by a SCSI device. It is a five-bit field which can be found in the first byte provided in response to an Inquiry Command...
that is polled every couple of seconds by e.g. the RAID controller software. Due to the low overhead required, impact on bus performance is negligible. For SAS
Serial Attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
or Fibre Channel
Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
systems, SAF-TE is replaced by the more standardized SCSI Enclosure Services
SCSI Enclosure Services
Most recent SCSI enclosure products support a protocol called SCSI Enclosure Services . The initiator can communicate with the enclosure using a specialised set of SCSI commands to access power, cooling, and other non-data characteristics.-SES devices:...
.
The most widely used version was defined in 'SAF-TE Interface Specification Intermediate Review R041497
April 14, 1997' by nStor (now Xyratex
Xyratex
Xyratex is a provider of disk drive manufacturing equipment and data storage subsystems with headquarters of Xyratex International in Havant, United Kingdom and U.S. headquarters in Fremont, CA. Xyratex has two business divisions serving distinct storage markets. They are the Networked Storage...
) and Intel.