SSD Latency Measurement via Internal Timestamping
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Solution Overview
Problem
Measuring latency of I/O operations in host computing systems is challenging due to resource consumption and interference from system software overhead and external noise, making it difficult to accurately separate storage device latencies from those introduced by the host computing system, storage fabric, and other components.
Innovation Solution
A solid state drive (SSD) records its own latency by timestamping I/O operations and maintaining a latency profile, allowing the host to determine I/O operation latencies without consuming host resources, and communicates this profile to the host upon request.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the host computing system measures latency of I/O operations, then latency measurement is performed, but host computing resources are consumed and measurement accuracy is reduced due to system software overhead and external noise
Solution Approach 1:
The latency measurement function is extracted from the host computing system and relocated to the storage device itself. The storage device independently measures its own I/O operation latencies using internal timing mechanisms, separating the measurement process from host resources and eliminating the interference of system software overhead and external noise that plague host-based measurements.
Solution Approach 2:
The storage device performs self-measurement of its own latency characteristics. By using internal timestamps and counters, the storage device autonomously captures latency data without requiring host computing resources, achieving both high measurement precision and zero host resource consumption.
2Measurement precision
If the host computing system measures latency of I/O operations, then latency data is obtained, but the measurement is affected by system software overhead and external noise
Solution Approach 1:
The measurement process is extracted from the host environment into the storage device's isolated internal environment. This physical and logical separation removes the measurement from the noisy host system context, eliminating the harmful effects of system software overhead, scheduler interference, and external noise that contaminate host-based latency measurements.
Solution Approach 2:
The storage device creates an inert measurement environment using its own internal clock and timing mechanisms. This self-contained measurement environment is immune to external disturbances, providing a clean baseline for latency measurement that accurately reflects only the storage device's performance characteristics.
3Loss of information
If latency measurement is performed in the host computing system, then latency data is collected, but it is difficult to separate storage device latencies from host-introduced latencies
Solution Approach 1:
By extracting the measurement function to the storage device, the patent creates a clear boundary between storage device latency and host latency. The storage device measures only its own internal processing time, while host transmission and processing latencies are naturally excluded, providing clean separation of latency sources without complex analysis.
Solution Approach 2:
The total I/O latency is segmented into distinct components: storage device latency (measured internally by the storage device) and host/fabric latency (occurring outside the storage device). This segmentation allows each component to be measured and analyzed independently, with the storage device providing precise measurement of its own contribution to total latency.
Data Source
AI summary
Provided are a method, apparatus, and a system for measuring latency of a storage device. The storage device measures one or more latencies of one or more input/output (I/O) operations received from a host. The storage device transmits information on the one or more latencies to the host.