Online Storage Volume Migration via Dual Volume Manager Transition
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Solution Overview
Problem
Existing storage systems face challenges in upgrading to newer data distribution techniques without significant downtime and excessive resource usage, as traditional methods require halting user applications or using entirely new storage devices.
Innovation Solution
Implementing a method where a first volume manager constrains a logical volume to a fixed subset of disks, transitioning control to a second volume manager that supports enhanced functionality, allowing online migration of data to new storage devices without interrupting host I/O requests.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional upgrade methods are used (halting user applications, backing up data, upgrading system, restoring data), then the system can be upgraded to newer data distribution techniques, but significant downtime occurs during the upgrade process
Solution Approach 1:
The system performs preliminary actions by creating a new logical volume with the newer data distribution technique (CRUSH mapping) before the upgrade. This new volume is prepared in advance with the target architecture, allowing seamless transition without halting user applications. The metadata is gradually redirected from the old mapping structure to the new one, enabling continuous operation during the upgrade process.
2Reliability
If traditional upgrade methods are used (using entirely new set of storage devices), then the system can migrate to newer data distribution techniques, but excessive storage capacity is required
Solution Approach 1:
The storage devices serve multiple functions during the transition period. The same physical storage devices are used by both the old logical volume (with traditional RAID mapping) and the new logical volume (with CRUSH mapping). This multi-functionality allows the system to upgrade data distribution techniques without requiring entirely new storage devices, thereby avoiding excessive storage capacity requirements.
3Reliability
If data migration is performed using traditional methods, then data can be moved from old storage devices to new storage devices, but user applications must be halted during the process
Solution Approach 1:
A new logical volume acts as an intermediary during the data migration process. This intermediary volume uses the newer CRUSH data distribution technique and serves as a bridge between the old and new systems. User applications continue to access data through this intermediary volume, which maintains data availability while enabling background migration and gradual redirection of metadata, thus preserving application continuity throughout the migration process.
Data Source
AI summary
Methods and structure for online migration of data in a storage system comprising a plurality of storage devices. The method comprises redefining a volume of a storage system mapped according to a first mapping structure by defining a second mapping structure. The method further comprises quiescing processing of host I/O requests directed to the volume and transitioning control of the volume from a first to a second volume manager so as to utilize the benefits of the second mapping structure. The method further comprises commencing processing of host I/O requests directed to the volume wherein the volume is mapped according to the second mapping structure. The method further comprises migrating, via the second volume manager, volume data to any of a plurality of storage devices of the system, online, without interrupting processing of host I/O requests directed to the volume. This migrates volume data without significant downtime or wasted space.