Selectively Transparent PCIe Bridge for Low Latency RAID Communication

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Solution Overview

Problem

Existing PCIe switching solutions fail to support low latency and efficient communication in RAID systems, leading to increased transaction latency and complexity due to the need for custom drivers and additional domain isolation, which negates the performance benefits of PCIe-based drives.

Innovation Solution

A selectively transparent PCIe bridge that allows direct transfer of transactions between the host and drive domains without address translation, using implicit or explicit address detection to route requests and completion transactions, ensuring seamless communication and management within the RAID controller.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a traditional multi-domain PCIe switch is used to isolate host and drive domains, then domain isolation and security are improved, but transaction latency increases due to address translation requirements

Engineering Contradiction:

Improvedomain isolationVSAvoidtransaction latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent extracts the address translation function from the PCIe switch by implementing a selectively transparent bridge that allows certain transactions to pass through without address translation. This separation enables domain isolation to be maintained for security while eliminating unnecessary address translation overhead for transactions that don't require it, thus reducing latency.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Instead of the conventional approach where all transactions between domains require address translation, the patent inverts the logic by making the bridge selectively transparent for transactions that don't need translation. This reversal of the default behavior (from requiring translation to allowing direct pass-through) reduces latency while maintaining isolation where needed.

Inventive Principle:

Principle #13The other way round (Inversion)

2Reliability

If address translation is implemented in the PCIe switch, then domain isolation is improved, but device complexity increases

Engineering Contradiction:

Improvedomain isolationVSAvoidswitch complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the address translation functionality from the PCIe switch fabric and implements it only where necessary in the selectively transparent bridge. This extraction reduces the overall complexity of the switch by removing unnecessary address translation logic from the main switch path while maintaining isolation capabilities where required.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent applies address translation only locally at the selectively transparent bridge for specific transactions that require domain isolation, rather than implementing it globally across the entire switch. This localized approach reduces overall device complexity by limiting the scope of complex address translation logic to only where it is needed.

Inventive Principle:

Principle #3Local quality

3Reliability

If custom drivers are required for domain communication, then domain isolation is improved, but ease of operation deteriorates

Engineering Contradiction:

Improvedomain isolationVSAvoiddriver configuration

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The selectively transparent bridge automatically determines whether address translation is needed for each transaction based on the transaction type and destination, without requiring custom driver intervention. This self-service approach simplifies operation by eliminating the need for complex custom drivers while maintaining domain isolation where necessary.

Inventive Principle:

Principle #25Self-service

4Loss of time

If a transparent PCIe switch is used for direct communication, then transaction latency is reduced, but domain isolation deteriorates

Engineering Contradiction:

Improvetransaction latencyVSAvoiddomain isolation

Core Design Contradiction:

Loss of timeVSReliability

Solution Approach 1:

The patent inverts the traditional transparent switch concept by making the bridge selectively transparent rather than fully opaque. Instead of blocking all direct communication and requiring address translation for all transactions, the selectively transparent bridge allows direct low-latency communication for transactions that don't require isolation while maintaining isolation for those that do.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS9753880B1Method and switch for transferring transactions between switch domains

Publication Date: 2017.09.05 MICROSEMI SOLUTIONS US INC

AI summary

The disclosure generally relates to a PCIe switch that includes a selectively transparent bridge that selectively allows transactions to traverse between multiple PCIe domains without the encumbrance of each root complex entity requiring knowledge of the selectively transparent bridge. The bridge that enables the transactions is invisible to the root complex entity in a host and drive switch domain of the PCIe switch. No address translation of the transactions is required because the drive switch domain address map is a subset of the host switch domain address map. The bridge allows for extremely low latency transactions between host systems and storage drives because the bridge allows the storage drive to read the Direct Memory Access (DMA) Scatter-Gather List (SGL) directly from host memory. The bridge also allows I/O data reads and writes from the storage drive directly to the host memory without store and forward within a RAID controller's memory.