New SAS 2.0 Features: Cabling, Connectors, And Value
10 Meter Cable Length
While SAS 1.1 at 3 Gb/s already supports cable lengths of up to 8 meters, SAS 2.0 at 6 Gb/s bumps this length to 10 meters. This may not sound like much, but it could prove beneficial in datacenters. To ensure reliable transfers, Decision Feedback Equalization (DFE) had to be introduced. This reduces inter-symbol interference and maintains signaling on a high level across a longer distance.
MiniSAS 4X Connectors
The days of the InfiniBand connector are numbered with SAS 6 Gb/s.
SAS 6 Gb/s requires mini-SAS, also known as iPass, connectors. Mini-SAS also works on 3 Gb/s links and is already available on many storage solutions.
Spread Spectrum Clocking
Varying clock speeds help to reduce electrical emissions so SAS can stay within FCC limits. If a wider range of frequencies is used, the peak amplitude of radiated emissions drops. This approach is required for 6 Gb/s SAS but not for the 3 Gb/s generation.
Value Proposition
This chart differentiates popular storage architectures for business and enterprise applications:
| Header Cell - Column 0 | Performance | Low Cost | High Distance |
|---|---|---|---|
| 4 Gb and 8 Gb Fibre Channel | Yes | - | - |
| iSCSI over Gigabit Ethernet | - | Yes | Yes |
| iSCSI over 10 Gigabit Ethernet | Yes | - | Yes |
| SAS 1.1 and 2.0 (3 and 6 Gb/s) | Yes | Yes | - |
Source: SCSI-TA.
The SCSI Trade Association positions SAS to coexist with Fibre Channel and iSCSI, but SAS clearly excels for value-oriented external solutions.
