Storage Cache Dirty Data Rate Control
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Solution Overview
Problem
Existing data storage systems face inefficiencies in managing bandwidth contention between write and sync operations in multi-tiered storage systems, leading to reduced write data operation speed and increased bypass to slower backend devices when cache space is fully dirty.
Innovation Solution
An apparatus and method that determine the amount of dirty data in the cache and adjust sync and write rates accordingly, using a processing module to accelerate write rates when dirty data is below a threshold and decelerate sync rates when it exceeds a threshold, employing Weighted Round Robin arbitration to prioritize operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sync rate is increased to maintain clean space in the cache, then the reliability of write-back caching is improved, but the write data operation speed deteriorates due to bandwidth contention
Solution Approach 1:
The patent implements dynamic rate adjustment where the sync rate and write rate are not fixed but adaptively changed based on the amount of dirty data in the cache. When dirty data is below a threshold, the sync rate is increased to maintain clean space, and when dirty data exceeds the threshold, the write rate is accelerated to utilize available bandwidth. This dynamic adjustment resolves the contradiction by allowing the system to optimize for reliability or speed depending on the current cache state.
Solution Approach 2:
The patent changes the operational parameters (sync rate and write rate) based on the dirty data amount in the cache. By monitoring the dirty data threshold and adjusting these parameters accordingly, the system can shift between prioritizing sync operations (when cache is mostly clean) and prioritizing write operations (when cache has accumulated dirty data), thus resolving the speed-reliability tradeoff.
2Productivity
If the write rate is accelerated to improve data storage speed, then the productivity is improved, but the sync operations may be delayed causing accumulation of dirty data
Solution Approach 1:
The system dynamically adjusts the write rate based on the current dirty data amount. When the dirty data is below the threshold, the write rate is accelerated to maximize productivity. When dirty data exceeds the threshold, the write rate is reduced to allow sync operations to catch up, preventing excessive accumulation of dirty data. This dynamic control resolves the contradiction between storage speed and sync delay.
Solution Approach 2:
The patent implements a feedback mechanism where the sync operation status (dirty data amount) is continuously monitored and used to adjust the write rate. This closed-loop control ensures that write operations are accelerated only when sync operations can keep up, and write operations are throttled when sync operations are falling behind, thus balancing productivity with timely synchronization.
3Productivity
If bandwidth is shared between write and sync operations, then the device utilization is improved, but the write data operation speed deteriorates due to contention
Solution Approach 1:
The patent implements periodic action by alternating between phases of accelerated write operations and phases of accelerated sync operations based on the dirty data threshold. During periods when dirty data is low, write operations receive prioritized bandwidth. When dirty data accumulates beyond the threshold, sync operations receive prioritized bandwidth. This periodic alternation resolves the contradiction by providing both high device utilization through continuous operation and high write speed during favorable conditions.
Solution Approach 2:
The system dynamically adjusts bandwidth allocation between write and sync operations based on the dirty data amount. Rather than fixed bandwidth sharing, the bandwidth allocation is flexible and adapts to the current system state, allowing write operations to utilize maximum bandwidth when sync operations have cleared sufficient space, thus resolving the speed-utilization tradeoff.
Data Source
AI summary
An apparatus for accelerating tasks during storage caching and tiering includes a processor. First and second storage units are coupled to the processor. A memory unit is coupled to the processor. The memory unit is configured to receive a write data operation. An amount of dirty data in the first storage unit is determined based on the received write data operation. The dirty data includes data present in the first storage unit to be synced to the second storage unit. A sync rate associated with a read data operation from the first storage unit to the second storage unit is decelerated when the amount of dirty data is less than a first threshold value. A write rate associated with a write data operation to the first storage unit is accelerated when the amount of dirty data is less than the first threshold value.