Write-Back Cache Aware Snapshot Creation

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Solution Overview

Problem

Combining snapshot and caching technologies can result in point-in-time inconsistent data, leading to unusable backups due to caching solutions like write-back caching, which store writes in cache memory instead of the storage device, causing data inconsistencies that snapshot solutions may overlook.

Innovation Solution

Implement a method to monitor writes stored in cache memory and ensure they are included in snapshots by tracking and flushing these writes to the backing store, allowing for write-back-cache aware snapshot creation that maintains data consistency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If write-back caching is implemented to improve storage system performance, then storage system performance is improved, but data consistency is worsened (point-in-time inconsistent data)

Engineering Contradiction:

Improvestorage system performanceVSAvoiddata consistency

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces a cache abstraction layer as an intermediary between the cache and the snapshot solution. This layer monitors writes stored in cache memory and coordinates with the snapshot creation process to ensure cached writes are included in snapshots, thereby maintaining data consistency while preserving the performance benefits of write-back caching

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The cache abstraction layer implements feedback mechanisms by monitoring which writes are stored in cache and providing this information to the snapshot creation process. This feedback loop ensures that snapshots include all relevant writes, including those temporarily stored in cache, thus resolving the data consistency issue

Inventive Principle:

Principle #23Feedback

2Loss of time

If snapshot creation is performed without cache awareness, then snapshot creation speed is improved, but snapshot data accuracy is worsened (point-in-time inconsistent snapshots)

Engineering Contradiction:

Improvesnapshot creation speedVSAvoidsnapshot data accuracy

Core Design Contradiction:

Loss of timeVSLoss of information

Solution Approach 1:

The cache abstraction layer performs preliminary actions by pre-monitoring and tracking writes to cache memory before snapshot creation is requested. This allows the snapshot solution to quickly retrieve the list of cached writes and include them in the snapshot without delaying the snapshot creation process, thus maintaining both speed and accuracy

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS9311242B1Systems and methods for enabling write-back-cache aware snapshot creation

Publication Date: 2016.04.12 ARCTERA US LLC

AI summary

A computer-implemented method for enabling write-back-cache aware snapshot creation may include (1) identifying a cache that implements write-back caching to selectively store at least one write to a backing store, (2) receiving, while the write is stored within the cache, a request to create a snapshot of the backing store, and (3) creating, in response to the request, the snapshot of the backing store by (a) determining that the write is stored within the cache and (b) tracking, in response to the determination, the write stored within the cache to ensure that the write is included in the snapshot of the backing store. Various other methods, systems, and computer-readable media are also disclosed.