Storage Array Reservation Forwarding for Seamless Data Migration
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Solution Overview
Problem
During data migration in a storage area network, existing technologies 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
1Reliability
If the destination storage system forwards SCSI reservations to the source storage system during data migration, then host access to storage volumes is maintained without disruption, but the complexity of managing competing reservations increases
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 to maintain access continuity without disrupting hosts while handling the complexity of competing reservations.
Solution Approach 2:
The destination storage system performs preliminary actions by establishing pass-through states and pre-configuring reservation forwarding mechanisms before data migration begins. This allows the system to proactively manage reservation conflicts and maintain host access without disruption during the migration process.
2Productivity
If the destination storage system operates in pass-through state to forward reservations, then data migration can proceed seamlessly, but the risk of reservation conflicts increases
Solution Approach 1:
The destination storage system implements feedback mechanisms by monitoring reservation requests and conflicts in real-time during data migration. When reservation conflicts are detected, the system can adjust its forwarding behavior, coordinate with the source storage system, and resolve conflicts to maintain both migration productivity and system reliability.
3Adaptability or versatility
If SCSI-3 persistent reservations with multiple keys are implemented, then multiple hosts can have controlled access to volumes, but the complexity of tracking and managing reservations increases
Solution Approach 1:
The reservation management system segments the complex task of tracking multiple SCSI-3 reservations by maintaining separate reservation states for different hosts and keys. The destination storage system independently tracks each host's reservation status and forwards relevant information to the source storage system, making the overall system more adaptable while managing complexity through modular state tracking.
Data Source
AI summary
A method is provided for a destination storage system to join a storage area network with a source storage system. The method includes discovering a volume on the source storage system when the source storage system exports the volume to the destination storage system and exporting the volume to the host computer systems. When a command to reserve the volume for a host computer system is received, the method includes determining locally if the volume is already reserved. When the volume is not already reserved, the method includes reserving locally the volume for the host computer system and transmitting to the source storage system another command to reserve the volume for the destination storage system.