Which PCIe slot must be used for a SAS HBA on R4B revision controllers?

While modern FlashArrays (like the XR4 and XL series) primarily use NVMe-oF/RoCE for backend connectivity, specific configurations or legacy support scenarios may still require a SAS HBA (Serial Attached SCSI Host Bus Adapter), for example, when connecting to older SAS-based expansion shelves during a migration or hybrid configuration.

For R4B revision controllers (a specific hardware revision of the Gen 4 controller), the strict hardware addressing map requires that any SAS HBA be installed in PCIe Slot 1 .

Slot 1 provides the specific PCIe lane routing and BIOS interrupts required for the legacy SAS controller to be recognized and function without conflicting with the native NVMe fabric.

Installing the card in Slot 0 (typically reserved for RoCE/Ethernet backend) or Slot 4 would likely result in the card being ignored by Purity or causing boot errors due to resource conflict.