Why does the StreamStor recorder use a PCI Express non-transparent bridge (NTB) for connection to a host system?

The cabled PCI Express (PCIe) non-transparent bridge (NTB) provides a high performance connection to the customer system for command/control and data upload or offload.  This capability establishes a PCIe Gen3 x8 (64 Gbps) connection over a distance of up to several meters.   There are also optical fiber implementations available to extend this connection over greater lengths.

 

The StreamStor recording system has its own self contained controller that is the root device for the recorder and in order for 2 PCIe roots (customer workstation and recorder) to be connected there must be a non-transparent PCIe bridge in between.  Standard PCIe expansion boards like the Keysight M9049A/M9048B boards simply extend the reach of a workstation root device out to additional PCIe devices in a chassis that does not have its own root device.  The NTB cabled PCIe solution makes the same physical connection but implements the NTB to translate between the 2 unique memory address spaces in each PCIe root.

 

The system is architected this way so that the hardware/software can run without having to share resources with other applications and devices in order to provide a deterministic environment.  This ensures that record/playback performance is delivered reliably.  In essence, the NTB makes the recording system look to the user system like just another PCIe device plugged into its bus.  If a transparent bridge was used, all of the software (including drivers) would have to run on the customer system and fight for resources with other applications and hardware.  It is possible to build a StreamStor system in that way but it has to be in a controlled/managed installation that is well tested so that bottlenecks do not occur that would cause loss of data in the playback/record process.  Since every application is different it would be unreasonable to do that every time so the recorder typically implements a dedicated processor that is isolated using the NTB.  Another benefit of this approach is that the recorder is self contained and does not require the customer workstation to operate.  It can be accessed and operated remotely over Ethernet but the system could also be automated in various ways to run without user intervention.

 

The latest cabled PCIe boards from Dolphin ICS utilize the SFF-8644 connectors (commonly called mini SAS) and allow the connection from a single customer workstation to as many as 4 StreamStor recording systems.  The StreamStor API provides an optional nodeid parameter when opening the connection to a recorder if multiple StreamStor systems are connected.  The nodeid of the customer workstation is typically set to 4 and the StreamStor systems use a starting nodeid of 8 with each additional system incrementing that by 4 (12, 16, etc).  Contact Conduant support for more information.