Sideband with External SAS Cable & Port Expander


the plan is to use an external SAS cable (SFF-8088 or SFF-8644 connectors) to connect an HBA to an external JBOD. The JBOD will contain a SAS expander card.
The exact models for the HBA, the cable, and the SAS expander are not decided, yet.

  • How will the sideband connection (to control the LEDs of the drives) behave in this scenario?
  • Are the sideband lines forwarded via the external SAS cable?
  • How will the sideband signals behave at the SAS Expander (is it generally possible to get the sideband signals “forwarded” over a SAS expander)?

Has someone here some experience on this topic?

Thanks a lot,


It should just work, if your equipment is sane.

Yes, though I think they’re not actually used to talk to the expander…

I think it’s the expander that handles those, based on the SCSI commands for the disks in question.

The expander handles the lights directly, but the HBA can tell it what to do.

The HBA should ask the expander (via SES) what it supports, and then send commands to change the light state based on what is supported by the expander.

One thing that is handled directly by the Supermicro expanders is the blue lights are lit solid for SAS drives but turned off for SATA drives. In either case, the lights blink based on activity, but reversed from each other (blink off for activity for SAS, blink on for SATA).

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