In computer storage, SAF-TE (abbreviated from SCSI Accessed Fault-Tolerant Enclosure) is an industry standard to interface an enclosurein-band to a (parallel) SCSI subsystem in order 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
A SCSI backplane with SCA-2 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 part of Seagate Technology) and Intel.
Command interface
Status requests are performed as READ BUFFERSCSI 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.
