Storage Array Reservation Forwarding for Seamless Data Migration
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Solution Overview
Problem
During data migration in a storage area network, existing systems face challenges in handling competing SCSI reservations without disrupting host access to storage volumes, especially when migrating data from a source storage system to a destination storage system.
Innovation Solution
The destination storage system operates in a pass-through state during the initial configuration phase, forwarding SCSI-2 and SCSI-3 reservations to ensure exclusive access for requesting hosts while maintaining continuous access for other hosts, using techniques like NPIV for Fibre Channel and virtual IP addresses for iSCSI to manage multiple paths and reservations efficiently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If the destination storage system forwards SCSI reservations to the source storage system during data migration, then host access continuity is maintained, but reservation conflict handling becomes complex
Solution Approach 1:
The destination storage system acts as an intermediary between hosts and the source storage system during data migration. It receives SCSI reservation requests from hosts, forwards them to the source storage system, and manages the reservation state locally. This intermediary role allows the system to maintain host access continuity by handling reservation conflicts at the destination layer without disrupting host operations, while the source storage system continues to serve data migration purposes.
2Productivity
If the destination storage system operates in pass-through state, then data migration proceeds smoothly, but exclusive access control for requesting hosts is compromised
Solution Approach 1:
The destination storage system dynamically adjusts its operational state between pass-through mode and reservation enforcement mode. During normal data migration operations, it operates in pass-through state to allow smooth data flow. When a host requests exclusive access, the system transitions to reservation enforcement state, setting local reservations to block other hosts. This dynamic state adjustment allows the system to balance data migration efficiency with exclusive access control requirements based on real-time needs.
3Adaptability or versatility
If multiple hosts access the same volume via both source and destination storage systems, then access flexibility is improved, but reservation conflicts increase
Solution Approach 1:
The system segments reservation management into two independent layers: source storage system reservations and destination storage system reservations. Each layer maintains its own reservation state independently. The source storage system manages reservations for hosts accessing data during migration, while the destination storage system manages reservations for hosts accessing data after migration. This segmentation allows multiple hosts to access volumes through both systems simultaneously with improved flexibility, while reservation conflicts are contained and managed separately at each layer rather than creating system-wide conflicts.
Data Source
AI summary
A method is provided for a destination storage system to handle SCSI-3 reservations. The method includes discovering a volume on a source storage system when the source storage system exports the volume to the destination storage system, exporting the volume to host computer systems, locally registering keys for first paths to the destination storage system, and registering with the source storage system the keys for second paths to the source storage system. When one of the host computer systems requests to reserve the volume, the method includes locally reserving the volume for paths to the destination storage system with registered keys and performing reservation forwarding to request the source storage system to reserve the volume for paths to the source storage system with registered keys.