SAF-TE

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In computer storage, SAF-TE (abbreviated from SCSI Accessed Fault-Tolerant Enclosure) is an industry standard to interface an enclosure to a (parallel) SCSI subsystem to gain access to information or control for various elements and parameters. These include 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[edit]

A SCSI backplane with SCA connectors inside an enclosure (SAF-TE device not visible)

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[edit]

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 information 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[edit]

  1. ^ a b SAF-TE IR 1.0 Introduction
  2. ^ a b SAF-TE IR 3.0 SAF-TE Interface
  3. ^ SAF-TE IR 2.0 SCSI Specification

See also[edit]

External links[edit]