File System Metadata Recovery Using Persistent Fast Storage
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Solution Overview
Problem
Conventional file system recovery is slow due to the large number of metadata objects being read, updated, and written back to disk, leading to non-deterministic write times and cache occupancy issues, which prolong file system recovery and hinder cache usage for user data objects.
Innovation Solution
Implementing a multi-tiered storage system that stores metadata blocks on a Solid State Disk (SSD) or other persistent fast storage, bypassing the volatile cache during file system recovery, and updating metadata objects directly in the persistent fast storage before returning them to disk storage, thereby disabling cache access during recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If metadata objects are stored on persistent disk storage and accessed via volatile cache, then cache can be used for user data objects, but file system recovery time is greatly prolonged due to reading, updating, and writing back large numbers of metadata objects
Solution Approach 1:
The patent segments the storage system into three distinct tiers: persistent disk storage for metadata objects, fast persistent storage (SSD) for recovery operations, and volatile cache for user data objects. This segmentation allows metadata to be isolated from the cache during recovery, preventing cache pollution while maintaining normal cache functionality for user data.
Solution Approach 2:
The patent introduces fast persistent storage (SSD) as an intermediary between persistent disk storage and volatile cache. During recovery, metadata objects are loaded from persistent disk to SSD, updated there, and then written back, bypassing the volatile cache entirely. This intermediary layer enables deterministic access times while preserving cache availability for user data.
2Reliability
If metadata objects are frequently read, updated, and written back to disk during recovery, then recovery can be performed, but write times become non-deterministic due to disk location, head movement, and channel bandwidth variability
Solution Approach 1:
The patent replaces mechanical disk storage with solid-state storage for metadata objects during recovery operations. SSDs provide deterministic access times without mechanical moving parts, eliminating variability caused by disk head movement and rotational latency. This substitution ensures predictable and consistent recovery times while maintaining complete metadata updates.
3Ease of operation
If large numbers of metadata objects occupy the fast cache during recovery, then metadata can be updated, but cache space for user data objects is reduced
Solution Approach 1:
The patent extracts metadata objects from the volatile cache during recovery operations and places them exclusively in fast persistent storage (SSD). This extraction prevents metadata from occupying cache space, ensuring the volatile cache remains fully available for user data objects while still enabling complete metadata update capabilities during recovery.
Data Source
AI summary
A system and method for providing a faster disk recovery is provided by bypassing the file system cache temporarily holding a sub set of metadata objects of the file system and instead using a persistent fast storage that can be accessed at deterministic speeds to hold all the metadata objects of the file system. The system speeds recovery by only writing updated metadata objects to the persistent disk storage when file system recovery is complete.