Data Storage Device Egress Buffer Cut-Through Latency
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Solution Overview
Problem
Conventional data storage devices (DSDs) experience transmission latency due to buffering all data for an entire frame before transmission, which affects system performance and resource sharing efficiency, especially in systems with multiple DSDs sharing a common bus.
Innovation Solution
Implementing a 'cut through' egress mode in the buffer controller circuitry allows for partial transmission of formatted data before all data is stored in the egress buffer, reducing latency and maintaining protocol integrity by using buffer controller circuitry to determine the egress mode based on data availability and formatter state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If data is buffered completely before transmission, then data integrity is maintained, but transmission latency increases
Solution Approach 1:
The system performs preliminary actions by pre-formating data and placing it in the egress buffer before transmission is needed. This allows the data to be ready for immediate transmission without waiting for the complete buffer to be filled, reducing latency while maintaining integrity through protocol-compliant formatting.
Solution Approach 2:
The buffer controller dynamically adjusts the egress mode between store-and-forward and cut-through based on real-time conditions. This dynamic switching allows the system to optimize between data integrity (store-and-forward) and transmission speed (cut-through) depending on the current operational state and data availability.
2Reliability
If store-and-forward mode is used, then data is transmitted completely before next transmission, but resource sharing efficiency decreases
Solution Approach 1:
The buffer controller dynamically switches between store-and-forward and cut-through egress modes based on system conditions. When multiple DSDs are sharing the bus, the system can use cut-through mode to improve resource sharing efficiency by allowing overlapping operations, while falling back to store-and-forward when data integrity is critical.
Solution Approach 2:
The cut-through mode enables continuous useful action by allowing the next frame to be formatted and prepared while the current frame is still being transmitted. This eliminates idle time between transmissions and improves the continuity of data flow, thereby enhancing resource sharing efficiency among multiple storage devices.
3Loss of time
If cut-through mode is implemented, then transmission latency is reduced, but protocol compliance may be compromised
Solution Approach 1:
The buffer controller uses feedback from the formatter state and data availability conditions to determine when cut-through mode is safe to use. The system continuously monitors whether the formatted data is ready and whether protocol requirements are met before switching to cut-through mode, ensuring protocol compliance is maintained while still achieving latency reduction.
Solution Approach 2:
The system changes operational parameters by switching between different egress modes (store-and-forward vs. cut-through) based on data availability and formatter state. This parameter change allows the system to optimize transmission performance when conditions permit while maintaining protocol integrity through controlled mode switching.
Data Source
AI summary
Data transmission from a data storage device (DSD) to a host. Data is received from a volatile memory of the DSD in an ingress buffer of the DSD and the data from the ingress buffer is formatted into formatted data. A size of data buffered in the ingress buffer is compared to a frame ingress size for data to be buffered in the ingress buffer for a frame to be transmitted to the host. It is determined based on the comparison whether to buffer all of the formatted data for the frame in an egress buffer of the DSD before transmission to the host, or to transmit at least a portion of the formatted data for the frame to the host before all of the formatted data for the frame is received in the egress buffer.