Software Fencing for Non-SCSI Shared Storage
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Solution Overview
Problem
Existing cluster systems face challenges in maintaining data integrity and high availability due to split-brain and amnesia conditions, particularly when using non-SCSI compliant storage devices like SATA and SSD, which lack SCSI-2 or SCSI-3 reservation features, making it difficult to implement effective fencing and quorum strategies.
Innovation Solution
A system and method that employs a polling thread on each node to monitor registration keys on a shared storage device, halting nodes that are no longer part of the cluster and using a cluster membership agent to manage node access, thereby providing fencing and quorum features independently of storage device hardware or firmware, allowing use of less-expensive storage devices like SATA and SSD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SCSI-2 or SCSI-3 reservation features are used for fencing, then data integrity is protected, but compatibility with non-SCSI compliant storage devices (SATA, SSD) is lost
Solution Approach 1:
The patent replaces the hardware-based SCSI reservation mechanism with a software-based fencing approach. Instead of relying on storage device hardware features, the system uses software processes to monitor registration keys and control node access to shared storage, enabling fencing functionality on non-SCSI compliant devices.
Solution Approach 2:
The invention creates a universal fencing mechanism that works across different storage device types (SCSI, SATA, SSD) by abstracting the fencing logic into software. The registration key-based system provides multi-functional capability to protect data integrity regardless of the underlying storage hardware.
2Reliability
If SCSI reservation system is used, then fencing is achieved, but device complexity increases due to hardware/firmware dependencies
Solution Approach 1:
The patent eliminates dependency on storage device hardware/firmware by implementing fencing purely in software. The system uses polling threads that read registration keys from shared storage to determine node access rights, removing the need for complex hardware reservation mechanisms.
Solution Approach 2:
The invention uses simple registration keys stored in shared storage as a lightweight fencing mechanism instead of complex hardware reservation systems. These software-based keys are easily created, modified, and removed, providing a simple and maintainable fencing solution.
3Reliability
If quorum strategy is implemented, then high availability is improved, but vulnerability to hardware changes increases
Solution Approach 1:
The patent makes the quorum strategy independent of storage hardware by implementing it through software-based registration key management. The quorum decision logic operates in software, reading and writing registration keys to shared storage, thereby eliminating vulnerability to hardware or firmware changes.
Data Source
AI summary
A system and method for controlling access to a shared storage device in a computing cluster having at least two nodes configured as cluster members provide fencing and quorum features without using the device controller hardware/firmware so fencing can be provided with storage devices that do not support disk reservation operations, such as with non-SCSI compliant disks. A polling thread on each node periodically reads a designated storage space on the shared storage device at a polling interval to determine if its corresponding node registration key is present, and halts the node if the key has been removed. A cluster membership agent removes a corresponding node registration key from the designated storage space of the shared storage device and publishes new membership information indicating that the corresponding node has departed the cluster only after delaying for a time period greater than the polling interval.