Snapshot Cache Write Acknowledgement Latency

Solution Overview

Problem

Conventional snapshot approaches in data storage systems are inefficient, leading to increased latency and performance impact due to the need to copy Copy on First Write (CoFW) data before acknowledging write operations, which delays data storage and acknowledgement.

Innovation Solution

A method and system that determine whether new data is a first update of original data, allowing it to be written to a cache memory location while the CoFW data is read into another cache location, enabling simultaneous provision of both data types to cache memory and confirming write operation completion without waiting for CoFW data copying to be complete.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the conventional snapshot approach reads original data from disk into cache before writing new data, then data consistency is maintained, but write operation latency increases significantly

Engineering Contradiction:

Improvedata consistencyVSAvoidwrite operation latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The system performs preliminary actions by pre-allocating cache buffers and preparing snapshot storage locations before the write operation completes. The original data is identified and reserved in the snapshot volume in advance, so that when the write operation needs to proceed, the data is already in position, eliminating the need to read from disk during the critical write path.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent introduces an intermediary mechanism - a cache buffer and snapshot metadata structure - that mediates between the production volume and snapshot volume. This intermediary allows the system to decouple the write operation from the actual data copying, enabling the write to be acknowledged immediately while the snapshot copy proceeds asynchronously through the intermediary cache structures.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the system waits for CoFW data copying to complete before acknowledging write operations, then data integrity is ensured, but normal file system operation performance deteriorates

Engineering Contradiction:

Improvedata integrityVSAvoidfile system operation performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs preliminary actions by pre-allocating cache buffers and preparing snapshot storage locations before the write operation completes. The original data is identified and reserved in the snapshot volume in advance, so that when the write operation needs to proceed, the data is already in position, eliminating the need to read from disk during the critical write path.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent enables continuous file system operations by allowing write acknowledgments to be issued without interruption while snapshot data copying continues in the background. The useful action of maintaining the snapshot is continued asynchronously, while the file system remains responsive to new operations, achieving continuity of both snapshot maintenance and file system productivity.

Inventive Principle:

Principle #20Continuity of useful action

3Manufacturing precision

If the system copies original data to snapshot storage before writing new data to cache, then snapshot accuracy is maintained, but write operation speed decreases

Engineering Contradiction:

Improvesnapshot accuracyVSAvoidwrite operation speed

Core Design Contradiction:

Manufacturing precisionVSSpeed

Solution Approach 1:

The system performs preliminary actions by pre-allocating cache buffers and preparing snapshot storage locations before the write operation completes. The original data is identified and reserved in the snapshot volume in advance, so that when the write operation needs to proceed, the data is already in position, eliminating the need to read from disk during the critical write path.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent inverts the conventional sequence by first writing the new data to the cache and production volume, then copying the original data to the snapshot volume afterward. This inversion maintains snapshot accuracy because the original data is captured after the write completes, while dramatically improving write speed since the copy operation no longer blocks the write path.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS9460010B1Method, data storage system and computer program product for managing copy on first write data for snapshot purposes

Publication Date: 2016.10.04 EMC IP HLDG CO LLC

AI summary

A data storage system, method and computer program product for managing copy on first write data for snapshot purposes are disclosed. In one embodiment, a determination is made whether new data is a first update of original data in a first section of a data storage device in response to receiving a write instruction to write the new data. The new data is provided to a first location of a cache memory and the original data to a second location of the cache memory. Providing the new data to the first location in the cache memory is not dependent on whether the original data has been copied from the data storage device. Further, the original data can be provided to the second location of the cache memory after new data is provided to first location of the cache memory. Completion of the write instruction is confirmed in response to providing the new data to the first location of the cache memory.