Adaptive Write Acknowledgment for SSD Storage Controllers
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Solution Overview
Problem
Current SSDs face challenges with write transactions due to either Immediate Write ACK (IWA) or Delayed Write ACK (DWA) mechanisms, leading to delayed high-priority writes, read Quality of Service (rQoS) impacts, and increased write amplification, especially at low queue depths.
Innovation Solution
Adaptive Write Acknowledgment (AWA) approach, which immediately acknowledges high-priority writes, reserves buffer space for coalescing, informs hosts of ideal write granularity, and controls memory die programming, minimizing padding and write amplification while managing read-write collisions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If Immediate Write ACK (IWA) is used, then write speed is improved, but buffer space availability deteriorates
Solution Approach 1:
The buffer is segmented into a reserved portion exclusively for high-priority writes and a non-reserved portion for other operations. This segmentation allows HP writes to immediately utilize the reserved buffer space without competing with other write operations, thereby maintaining both write speed and buffer space availability.
2Quantity of substance
If Delayed Write ACK (DWA) is used, then buffer space availability is improved, but write speed deteriorates
Solution Approach 1:
Different acknowledgment policies are applied to different priority levels of writes. High-priority writes receive immediate acknowledgment from the reserved buffer portion, while other writes use delayed acknowledgment from the non-reserved portion. This local differentiation resolves the contradiction by providing fast acknowledgment where needed while maintaining overall buffer availability.
3Reliability
If high-priority writes are immediately acknowledged, then read Quality of Service is improved, but write amplification increases
Solution Approach 1:
Multiple high-priority writes are merged/coalesced into a single NAND programming operation when they arrive within a coalescing window. This merging reduces the number of separate programming operations needed, thereby reducing write amplification while still providing immediate acknowledgment to the host for each individual write request.
4Speed
If buffer space is reserved for high-priority writes, then high-priority write performance is improved, but low-priority write performance deteriorates
Solution Approach 1:
The buffer allocation is dynamic rather than static. The reserved portion is allocated specifically for high-priority writes when needed, while the non-reserved portion handles other writes. This dynamic allocation allows the system to optimize for high-priority performance when required while still accommodating low-priority writes in the non-reserved portion, preventing permanent degradation of low-priority performance.
Data Source
AI summary
Examples include techniques for managing high priority (HP) and low priority (LP) write transaction requests by a storage device. An embodiment includes receiving, at a storage controller for a storage device, a write transaction request from a requestor to write data to one or more memory devices in the storage device. When the write transaction request is for a high priority (HP) write, coalescing the write data into a transaction buffer in a memory of the storage device, sending an acknowledgment for the write transaction request to the requestor, and writing the write data into the one or more memory devices. When the write transaction request is for a low priority (LP) write, writing the write data into the one or more memory devices, and then sending an acknowledgment for the write transaction request to the requestor.