Virtual Hot Spare Cache Provisioning for RAID

Solution Overview

Problem

Conventional data storage systems face challenges in managing data storage during disk failures, as physical hot spares introduce location-dependent issues and do not improve performance during degraded modes, while existing RAID configurations are limited by the physical location of disks and do not efficiently utilize cache resources.

Innovation Solution

A Flash-based Cached Universal Hot Spare (CHS) is created as a virtual device from unused cache slots, allowing decoupling of the rebuild process from user access and providing a location-independent sparing function, which can be used in conjunction with hard-disk based hot sparing for enhanced performance and automation of the rebuild/repair cycle.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If physical hot spares are used in conventional data storage systems, then data availability during disk failures is improved, but system complexity and location-dependent issues increase

Engineering Contradiction:

Improvedata availability during disk failuresVSAvoidsystem complexity and location dependence

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent creates a virtual hot spare device by copying the sparing function into the cache subsystem rather than using a physical hot spare disk. The virtual hot spare is formed by allocating cache slots that can store data during a disk failure, effectively copying the hot spare functionality into existing cache infrastructure. This eliminates the need for additional physical hot spare devices while maintaining data availability during failures.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent transitions from a physical hot spare approach (three-dimensional spatial arrangement of disks) to a virtual hot spare approach that utilizes the cache subsystem's storage capacity. By provisioning cache slots as a virtual hot spare device, the system moves the sparing function from the physical disk layer to the cache layer, achieving location independence and reducing physical complexity.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If RAID configurations are used with physical hot spares, then data redundancy is improved, but performance during degraded modes remains limited

Engineering Contradiction:

Improvedata redundancyVSAvoidperformance during degraded modes

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent implements preliminary action by pre-allocating cache slots specifically for hot spare functionality before a disk failure occurs. These cache slots are reserved and configured in advance to serve as the virtual hot spare device. When a disk failure happens, the system can immediately utilize these pre-prepared cache slots without delay, improving response time and maintaining performance during degraded mode operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent makes the cache subsystem multi-functional by enabling it to serve both its normal caching function and the hot spare function simultaneously. The same cache hardware is used for both performance optimization (caching frequently accessed data) and reliability (storing data during disk failures). This universality allows the system to maintain high performance during normal operation while providing robust redundancy during failures.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If multiple physical hot spares are deployed, then data availability is improved, but device complexity and cost increase

Engineering Contradiction:

Improvedata availabilityVSAvoidnumber of physical components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent makes the cache subsystem multi-functional by enabling it to serve both its normal caching function and the hot spare function simultaneously. The same cache hardware is used for both performance optimization (caching frequently accessed data) and reliability (storing data during disk failures). This universality allows the system to maintain high performance during normal operation while providing robust redundancy during failures.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent creates a virtual hot spare device by copying the sparing function into the cache subsystem rather than using a physical hot spare disk. The virtual hot spare is formed by allocating cache slots that can store data during a disk failure, effectively copying the hot spare functionality into existing cache infrastructure. This eliminates the need for additional physical hot spare devices while maintaining data availability during failures.

Inventive Principle:

Principle #26Copying

Data Source

PatentUS9037795B1Managing data storage by provisioning cache as a virtual device

Publication Date: 2015.05.19 EMC IP HLDG CO LLC

AI summary

There is disclosed herein techniques for use in managing data storage in a data storage system comprising a cache and data storage devices. In one embodiment, the technique comprises setting a hot spare capacity value for a virtual hot spare device in a data storage system. The technique also comprises detecting the state of data storage devices in a RAID configuration in the data storage system. The technique further comprises determining if a cache in the data storage system has free capacity corresponding to the hot spare capacity value in response to detecting a failure state in connection with at least one of the data storage devices in the RAID configuration. The technique still further comprises provisioning at least a portion of the cache as the virtual hot spare device with a capacity corresponding to the hot spare capacity value in response to determining the cache has free capacity corresponding to the hot spare capacity value.