Coordinator Node Quiesce Mechanism for Crash-Consistent Distributed File System Clones
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Solution Overview
Problem
In distributed file systems, generating crash-consistent clones of files is challenging due to the asynchronous completion of file stripes across different nodes, leading to inconsistent clones when cloning requests are made between completion times of different stripes.
Innovation Solution
A method involving a coordinator node that identifies nodes storing file stripes, sends quiesce commands to ensure all write operations are complete, generates clones, and then unquiesces or aborts the process based on status, ensuring a consistent clone is created without affecting latency-sensitive applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If files are striped across different nodes in a distributed file system, then storage capacity and I/O performance are improved, but clone consistency deteriorates because stripes complete at different times
Solution Approach 1:
The system performs preliminary actions by quiescing the source file before cloning begins. This ensures all write operations are completed and flushed to disk before the clone operation starts, guaranteeing that the clone captures a consistent state of the file across all stripes without requiring synchronous completion during the clone operation itself.
Solution Approach 2:
The patent introduces an intermediary quiesce/unquiesce mechanism that mediates between the source file and the clone operation. The quiesce command acts as a barrier that ensures all data is safely written before cloning, while the unquiesce command restores normal operations after cloning completes, resolving the consistency issue without blocking I/O during the actual clone.
2Reliability
If quiesce commands are sent to ensure all write operations complete before cloning, then clone consistency is improved, but I/O latency worsens due to blocking write operations
Solution Approach 1:
The quiesce operation is performed as a preliminary action before the clone operation begins. By flushing and completing all pending write operations before cloning starts, the system ensures consistency without causing latency during the actual clone or subsequent I/O operations. The latency is confined to a brief window before cloning, not during it.
Solution Approach 2:
The system dynamically transitions the file through different states: quiesced (write-only), cloning (read-only), and unquiesced (normal I/O). This dynamic state management allows the system to temporarily block writes only when necessary for consistency, then immediately restore full I/O performance after cloning completes, minimizing overall latency impact.
3Manufacturing precision
If the cloning process waits for all stripes to complete before generating the clone, then clone accuracy is improved, but cloning time worsens and affects latency-sensitive applications
Solution Approach 1:
The system performs the quiesce operation as a preliminary action that ensures all stripes are fully written and consistent before cloning begins. Once quiesced, the clone operation can proceed immediately without waiting for stripe completion, as the quiesce has already captured the consistent state. This separates the consistency guarantee from the cloning duration.
Solution Approach 2:
The cloning process is segmented into distinct phases: quiesce (ensure consistency), clone (copy data), and unquiesce (restore operations). By segmenting the process, the system can ensure accuracy in the quiesce phase without letting it extend the cloning phase, allowing parallel execution of clone operations across multiple stripes without coordination overhead.
Data Source
AI summary
Techniques for generating a crash-consistent clone of file(s) stored by a distributed file system are described herein. To generate the crash-consistent clone, a coordinator node may identify multiple nodes (e.g., at least a first node and a second node) of the distributed file system that are storing different portions of data of the file. The coordinator node may then send a first command to the multiple nodes to cause each of the multiple nodes to quiesce the file and clone the different portions of the data to generate the crash-consistent clone of the file. The coordinator node may then receive, from the multiple nodes, a status associated with generating the crash-consistent clone of the file. Based at least in part on the status, the coordinator node may send a second command to the multiple nodes to cause each of the multiple nodes to unquiesce the file.