Persistent SCSI Device File Mapping via Unique Identifier
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The Linux SCSI subsystem lacks persistence of device file mappings across reboots, leading to potential issues with device identification and mounting of file systems, as minor numbers can change, causing inconsistencies in /etc/fstab and affecting automatic mounting of partitions.
Innovation Solution
The creation of unique logical unit identifier (UID)-based device file names that are independent of the SCSI path information, ensuring that device files remain consistent even after a reboot by using IOCTLs to generate identifiers and map them to persistent names.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If device files are assigned based on SCSI path information (host, bus, target, lun), then device identification is straightforward and follows standard conventions, but device file mappings change after reboots causing inconsistency
Solution Approach 1:
The patent changes the identification parameter from dynamic SCSI path information (host, bus, target, lun) to a static unique identifier (WWN) that remains constant across reboots. This parameter change ensures device file persistence while maintaining simple device identification through the use of invariant identifiers.
Solution Approach 2:
The patent introduces a unique identifier (WWN) as an intermediary between the SCSI device and the device file system. This intermediary serves as a stable reference that decouples the device file mapping from the dynamic SCSI path information, allowing consistent device identification independent of bus topology changes.
2Adaptability or versatility
If minor numbers are assigned dynamically to SCSI devices, then device allocation is flexible and adapts to system changes, but device file names change after reboots affecting /etc/fstab consistency
Solution Approach 1:
The patent changes the basis for minor number assignment from dynamic SCSI path parameters to a static unique identifier (WWN). This ensures that while device allocation remains flexible, the resulting device file names are stable across reboots because they are derived from invariant device identifiers rather than dynamic bus topology information.
3Productivity
If device files are created during boot based on current SCSI configuration, then initial device mapping is established quickly, but subsequent reboots may reassign devices causing mounting failures
Solution Approach 1:
The patent uses the unique identifier (WWN) as an intermediary to establish device file mappings during boot that are independent of SCSI path configuration. This intermediary ensures that device files are consistently created for the same physical devices across reboots, enabling reliable automatic mounting while maintaining efficient boot-time initialization.
Solution Approach 2:
The patent performs preliminary device identification using unique identifiers during the boot process, establishing device file mappings before the system needs to mount file systems. This preliminary action using invariant identifiers ensures that subsequent mounting operations can proceed reliably without device reassignment issues.
Data Source
AI summary
The method and apparatus is utilized in order to generate a persistent path to a SCSI device for a host. In an embodiment, a SCSI device is queried for path information related thereto, and if path information is returned, a SCSI command requesting identifier data is issued to the SCSI device. The identifier data is used to determine a unique identifier (UID), from which is generated a UID-based device file for the SCSI device that is independent from the path information.