PowerVault MD24: Amber SAS port link LED on enclosure connected with SAS-3 cable or 12Gb endpoint

24Gb SAS incorporates a new encoding method that improves link efficiency to meet the requirements of the 22.5 Gb/s line rate. This new method  incorporates 128b/130b encoding, plus 20-bit forward error correction (FEC), which allows 24G SAS to achieve the same signal integrity requirements as 12Gb/s SAS even though it is transferring data at twice the rate.    

To connect MD24 series enclosure to a PERC or SAS host bus adapter (HBA) use 24G mini-SAS HD (SFF-8674) to mini-SAS HD (SFF-8674) 36-pin cables. Supported I/O cables are listed in the Dell PowerVault MD24 Series Enclosure Support Matrix .

Note: SFF-8674 connectors are plug compatible with SFF-8644 connectors used in SAS-3 cable.  Look for the Dell part number label attached to the mini-SAS HD cable and compare it to supported IO cables listed in the Dell PowerVault MD24 Series Enclosure Support Matrix.

Aside from the Dell part number users can visually identify the difference between a Dell supplied SAS-3 and SAS-4 cables. The SAS-3 cable has a blue pull-out tab and the SAS-4 has a white pull-out tab.

Figure 1.   Comparison of Dell supplied SAS-3 and SAS-4 mini-SAS HD cables

PowerVault MD24 series enclosures have been validated with the following HBAs:

The following examples are used to illustrate the expected behavior when connecting different HBA and SAS cable configurations.  For cabling guidelines see the section Storage enclosure rules in the Dell PowerVault MD24 Series Enclosure Support Matrix .


In the following picture the MD24 expander management module (EMM) is connected using a 24G SAS specification cable on port 1 and is using a SAS-3 endpoint such as an HBA355e or a PERC H840 adapter, the LED shows amber because it negotiated a link speed less than 24G.   Port 2 is chained to another MD series array that has negotiated 24Gb link using a SAS-4 mini-SAS HD cable, the LED link is green. 
 

Figure 2.   SAS connections to MD24 EMM
 

In the following example the MD24 EMM port 1 is connected using a SAS-3 cable to a H965e PERC. Even though the H965e PERC supports 24Gb it is connected using a SAS-3 specification mini-SAS HD cable and fails to negotiate 24Gb link speed.

Figure 3.   SAS connections to MD24 EMM

Where no SAS LED link appears check the following items:

1. MD24 enclosure EMM is connected to a supported HBA and the cable is secure.  Give a gentle tug to verify that the mini-SAS HD connector is locked in position at both ends.   The slot position of the PCI-e HBA within the PowerEdge server may sometimes obstruct the insertion of the mini-SAS HD connector for more information see PowerEdge 16G models: HBA355e PCI-e Slot Selection
2. Both MD24 enclosure and connected PowerEdge host server must be powered up with the host operating system loaded.
3. PowerEdge PERC or SAS HBA firmware should be at minimum or latest support versions.
4. PowerEdge host operating system must load driver support for PERC or SAS HBA.