Vintage Computing

SAS Technology

SAS Technology

1. What is SAS

SAS – Serial Attached SCSI, A natural transition from parallel SCSI to serial

2. Why Serialize?

Signal skew and crosstalk; Signal termination restrictions; Cable and connector reflections;
Device addressability

3. SAS Performance

3.0Gbps(300MB/s)per single SAS port; Port Aggregation, eg. Combine 4 ports to a single
12Gbps WIDE PORT (x4 port); Full Duplex (24 Gbps); Multiple Initiators and Targets (with
Expander); Advanced Command Queuing

4. SAS Features/Benefits

Flexibility (Coexist of SAS and SATA Drives; SCSI software/middleware can be used);
Scalability (Up to 16,256 SAS/SATA devices in one SAS Domain; Expander is able to
connect 128 devices); Reliability (Dual Port and Multi-initiator for Fault Tolerance; Hotswap
connector; High MTBF Drive)

5. Advantage of SAS Interface

High Speed Serial SCSI instead of Parallel; Point-to-Point Connection; Expander for
Scalability; Dual Port Connectivity; SATA Compatible Dual 7-pin Interface; Port
Aggregation e.g. x4 WIDE PORT

6. What is a SAS Expander?

SAS devices:
(1)end devices:
SAS initiator devices (hosts), SAS target devices (peripheral devices) , and SATA devices
(2) expander devices:
edge expanders (sets), and fan-out expanders
Expander devices are the intermediary devices that allow more than one initiator to have a
connection to more than one target.

7. Interface Comparison

                     ATA           SATA                     SCSI           SAS       FC

Interface       Parallel      Serial                      Parallel       Serial    Serial

Addressing    2               1 or 16 w/ SATAII   16               128       16 million

Connection   80-pin        7-pin                       68-pin         7-pin     Copper/optical

Dual-port      No              No                           No               Yes       Yes

Duplex           Half           Half                          Half             Full       Full

Cable length   0.4m        1m                            12m            10m     30m(copper)300m(optical)

 

8. Maximum devices that can connect to SAS

16,256 with expanders

9. SAS appliaction

Midrange and enterprise servers

10. SAS topology

Point-to-point w/ expanders

 

SAS Technology

About the Author

AT-1 Automatic Labeling System f SCSI Cable