SAF-TE

In computer storage, SAF-TE (abbreviated from 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 for various elements and parameters, including temperature, fan status, slot status (populated/empty), door status, power supplies, alarms, and indicators (e.g. LEDs, LCDs).[1] Practically, any given SAF-TE device will only support a subset of all possible sensors or controls.[2]

Scope

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 (SEP) is represented as a SCSI processor device that is polled every few seconds by e.g. the RAID controller software.[1] Due to the low overhead required, impact on bus performance is negligible.[3] For SAS or Fibre Channel systems, SAF-TE is replaced by the more standardized SCSI Enclosure Services (SES).

The most widely used version was defined in the SAF-TE Interface Specification Intermediate Review R041497, released on April 14, 1997 by nStor (now Seagate Technology) and Intel.

Command interface

Status requests are performed as READ BUFFER SCSI commands, enclosure action requests as WRITE BUFFER commands.[2]

Command type Opcode mandatory / optional Command Description
READ BUFFER 00h m Read enclosure configuration inquire about system components in the enclosure
01h m Read enclosure status inquire about operational status of enclosure components
02h o Read usage statistics fetch information about total usage time and number of power-cycles
03h o Read device insertions returns information on how many times a device has been inserted into each enclosure slot
04h m Read device slot status returns infomation on the current state of each slot
05h o Read global flags read global flags from processor
WRITE BUFFER 10h m Write device slot status updates state of the slots, essentially drives LEDs, alarms etc.
11h o Set SCSI ID set the SCSI ID of any device on the channel
12h m Perform slot operation prepare a slot for insertion or removal (electronically or mechanically)
13h o Set fan speed set rotational speed for each fan
14h o Activate power supply turn a power supply on or off
15h m Send global flags send global flags to processor (audible alarm; indicators for global failure, global warning, enclosure power, fan/cooling failure, power failure, drive failure, drive warning, array failure, array warning; enclosure lock; enclosure identification)

References

  1. 1 2 SAF-TE IR 1.0 Introduction
  2. 1 2 SAF-TE IR 3.0 SAF-TE Interface
  3. ↑ SAF-TE IR 2.0 SCSI Specification

See also

External links


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