By: Jay Neer, Molex, SCSI Trade Association Board Member-at-Large
A number of new multi-sourced, intermateable connector products are queued up for the release of the INCITS T10 12Gb/s SAS standard. These new storage connectivity components enable end-to-end integration of the architectural and protocol enhancements for 12Gb/s SAS. Systems providers and integrators will have solutions that are twice as dense, twice as fast, more versatile, and extend farther than previous generations of SAS. Figure 1 provides a high level view of the new, end-to- end connectivity solutions involved.
The SAS switch shown in Figure 1 above, accepts passive copper cables, active copper cables and active optical cable assemblies. These cables plug into a bank of up to (32) 4x ports shown implemented as (8) 1×4 receptacles in Figure 2 below which creates the highest density 4x pluggable solution currently available in the market.
Pluggable solutions typically provide the option of connecting with either copper or optical cables. Mini-SAS HD’s multi-plugging feature however, also enables connections with either 4x or 8x cables. 4x cables can plug into any 4x port and 8x cables can plug into any two adjacent 4x ports. This feature provides a wider pipe without the need to create additional hardware SKU’s to accommodate the additional bandwidth. Figure 3 illustrates an example of the multi-plugging solution feature enabled with the Mini-SAS HD – for both external and internal I/O’s.
The physical size of the new double density requirement was constrained to match the size of the opening previously defined for the low profile PCIe card. Doubling the density of the existing Mini-SAS I/O was achieved by stacking two half-wide Mini-SAS receptacles within a single housing. The construction of the receptacle housings was switched from a die-cast design to a narrower stamped and formed solution to keep within the width and height constraints. Figure 4 shows the density of Mini-SAS HD compared to the current Mini-SAS.
The design of the 4x cable includes independent 2x cables terminated to individual paddle cards within the plug housing. This easily facilitates fail-over / high-reliability function for systems. One end of the cable would be plugged to the 4x storage port while the other end, which already exits the plug housing as two separate cables, can be readily connected to two different host ports, thereby enabling fail-over functionality. See Figure 5.
The two cable implementation provides additional benefits though improved cable management. The smaller diameter 2x cables have smaller bend radii and are therefore much more flexible than a single 4x cable design – see Figure 6. For implementations that prefer a single cable solution, flexible sleeving can be assembled over the 2x cables to provide the look of a single cable while maintaining the benefits of the additional flexibility. The use of multiple 2x cables can also be a very desirable method of implementing 8x cable assemblies as a single 8x cable could be quite stiff.
The internal connector and cabling solutions for Mini-SAS HD provide similar benefits for 12Gb/s SAS within enclosures. The double density and double data rate attributes also apply to the internal solutions. The receptacle connector itself is identical for both – the difference being the internal receptacles are assembled to a plastic frame whereas the external is assembled to a shield / shell. Figure 7 provides an illustration of the internal Mini-SAS HD compared to Mini-SAS.
The internal connections on the “front-side” of the mid-plane are shown in Figure 1.
The “back-side” of the mid-plane incorporates three new, application-dependent receptacles. The first is a new 12Gb/s SAS dual-port version that is a drop-in replacement for the 6Gb/s SAS receptacle. The second is a 12Gb/s SAS quad-port version; known as a MultiLink™ receptacle. The third is a new multifunction receptacle that enables either SAS or PCIe to operate through a common connector. Figure 8 shows the design progression from dual port to multifunction. Featuring plug-in compatibility, aAll dual, quad and multi-protocol device plugs intermate with all receptacles.
The preceding information provides an overview of the end-to-end, advanced-connectivity initiatives incorporated in the forthcoming release of the 12Gb/s SAS standard. These initiatives offer a number of benefits, including:
- Consolidating multi-source interfaces on a pluggable, double density, double data-rate, copper and optical external I/O with 4x/8x multi-plugging
- Consolidating multi-source interfaces on a double density, double data-rate, copper internal I/O with 4x/8x multi-plugging
- Release of a new mid-plane interconnect system enabling multiple 2.5″ pluggable storage and protocol options such as 12Gb/s Dual Port SAS, 12Gb/s MultiLink (Quad Port) SAS, and a Multifunction version that ports 12Gb/s Quad Port SAS or 8GT/s PCI Express. These options include both HDDs and SSDs.