Fractional Channel Multiplexing for SAS Bandwidth Utilization
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Solution Overview
Problem
Current Serial Attached SCSI (SAS) technologies face inefficiencies in bandwidth utilization, particularly when using higher-speed links for lower-bit-rate connections, leading to suboptimal system performance due to inability to leverage full available bandwidth.
Innovation Solution
The implementation of fractional channel multiplexing (FCM) in SAS systems, which dynamically schedules and multiplexes packets across multiple virtual lanes, optimizing bandwidth utilization by allocating time slots based on the maximum physical link rate supported by each target device, and using additional FCM bits to identify packet affiliation, allowing for efficient data interleaving and balanced throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a high-speed SAS-4 link is used for a lower-speed SAS-2 connection, then the connection can be established, but bandwidth utilization becomes very low (only 6 Gb/s from 22.5 Gb/s lane)
Solution Approach 1:
The patent divides the single high-speed SAS-4 link into multiple virtual lanes (SAS-4a, SAS-4b, etc.) that can be independently allocated to different devices. This segmentation allows the link to be shared among multiple targets, enabling a single initiator to maintain multiple connections at different speeds simultaneously, thus improving bandwidth utilization when connecting devices with different SAS generation capabilities
Solution Approach 2:
The patent introduces a new dimension of multiplexing by creating virtual lanes that operate in parallel over the physical link. Instead of a single time-division multiplexed channel, the system creates multiple logical channels that can be dynamically allocated, adding a layer of abstraction that enables better bandwidth utilization across devices with different speed requirements
2Productivity
If fractional channel multiplexing is implemented to improve bandwidth utilization, then bandwidth utilization efficiency increases, but device complexity increases due to additional FCM bits and scheduling mechanisms
Solution Approach 1:
The FCM bits are integrated into the existing SAS packet structure, allowing the same physical link and protocol to serve multiple functions: standard SAS communication and fractional channel multiplexing. This multi-functionality approach avoids creating separate complex signaling channels while still enabling virtual lane allocation and bandwidth optimization
Solution Approach 2:
The patent modifies the SAS packet format by adding FCM bits that encode virtual lane identification information. This parameter change allows the system to dynamically allocate bandwidth to different virtual lanes without fundamentally changing the underlying SAS protocol, thereby managing complexity through incremental modification rather than complete protocol redesign
Data Source
AI summary
Methods, devices, and systems relating to Serial Attached SCSI (SAS) storage interconnect technology are provided. An SAS serial connection is established between an SAS initiator and an SAS expander over a physical link for communications between the SAS initiator and a plurality of target devices. The plurality of target devices is in communication with the SAS expander. SAS packets associated with each of the plurality of target devices are dynamically multiplexed and transmitted over the single SAS serial connection. Each SAS packet comprises one or more information bits indicating the target device with which the SAS packet is associated. The dynamically multiplexed SAS packets transmitted over the SAS connection may comprise SAS packets associated with at least two target devices having different maximum physical link rates. A result may be improved bandwidth utilization of the physical link when legacy SAS target devices with slower physical link rates are utilized.