Export FSID Mapping for Seamless File Handle Preservation
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Solution Overview
Problem
Conventional data storage systems assign unique file system identifiers (FSIDs) that differ between systems, causing file handles to become ineffective when file systems are copied or migrated, leading to disruptive remounting and downtime during failover or migration events.
Innovation Solution
Introducing an export FSID (E-FSID) that is shared across data storage systems, allowing file handles to remain valid by mapping E-FSID to local FSID, enabling seamless failover and migration without disrupting client access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a file system is copied to a second data storage system, then the file system can be accessed from the second system, but the FSID assigned by the second system differs from the original FSID, causing file handles to become ineffective
Solution Approach 1:
The patent introduces an export FSID (E-FSID) as an intermediary identifier that bridges the original file system and its copies across different storage systems. The E-FSID is included in file handles and serves as a stable reference that clients use to access files regardless of which storage system they connect to. Each storage system maintains a mapping between the E-FSID and its local FSID, allowing the same file handle to work across system boundaries without requiring remounting.
2Adaptability or versatility
If the FSID is changed when copying a file system, then the second data storage system can independently identify its copy, but client file handles must be remounted causing disruption
Solution Approach 1:
The patent performs preliminary actions by pre-establishing the E-FSID mapping in the second storage system before the actual file system copy operation completes. The export FSID is assigned and registered in advance, so that when the file system copy is finished, the mapping is already in place and ready to receive file handles. This preliminary setup eliminates the need for post-copy remounting operations and avoids client disruption.
3Device complexity
If each data storage system uses its own local FSID, then the system can maintain simple internal identification, but cross-system file access requires remounting operations
Solution Approach 1:
The patent segments the file system identification into two distinct parts: the export FSID (E-FSID) that is visible to clients and used in file handles, and the local FSID that is used internally by each storage system. This segmentation allows each storage system to maintain its simple local FSID scheme while simultaneously supporting cross-system access through the separate E-FSID layer. The mapping between E-FSID and local FSID acts as a translation layer that preserves both internal simplicity and external continuity.
Data Source
AI summary
A technique for managing access to files by different data storage systems includes a data storage system generating an E-FSID (export FSID) for a file system in addition to a conventional FSID and providing the E-FSID in file handles that the data storage system generates for providing clients with access to the file system. The E-FSID is shared between/among different data storage systems, with each data storage system including data for cross-referencing the E-FSID to a respective local FSID for the file system. Because the E-FSID for a file is the same across different data storage systems, file handles continue to work after failover, migration, and other transitions.