Soft updates: A solution to the metadata update problem in file systems
Soft updates: A solution to the metadata update problem in file systems
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DOI：
10.1145/350853.350863
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发表时间：
2000-05-01
影响因子：
1.5
通讯作者：
Patt, YN
中科院分区：
文献类型：
--
作者：
Ganger, GR;McKusick, MK;Patt, YN
元数据更新（例如文件创建和块分配）一直被认为是文件系统性能、完整性、安全性和可用性问题的根源。软更新是一种对回写式缓存块进行细粒度更新的低成本排序的实现技术。使用软更新来跟踪和强制执行元数据更新依赖性，文件系统可以安全地对几乎所有文件操作使用延迟写入。本文介绍了软更新、将它们合并到 4.4BSD 快速文件系统中以及对系统产生的影响。我们证明，使用软更新的基于磁盘的文件系统可以实现基于内存的文件系统性能，同时提供比大多数基于磁盘的文件系统更强的完整性和安全性保证。对于经常对元数据执行更新（例如创建和删除文件）的工作负载，与传统的同步写入方法相比，性能提高了两倍以上，最高可达 20 倍；与激进的预写日志记录方法相比，性能提高了 4-19%。此外，软更新可以通过将崩溃恢复辅助（例如 fsck 实用程序）降级为可选的后台角色来提高文件系统可用性，从而将文件系统恢复时间缩短到不到一秒。
Metadata updates, such as file creation and block allocation, have consistently been identified as a source of performance, integrity, security, and availability problems for file systems. Soft updates is an implementation technique for low-cost sequencing of fine-grained updates to write-back cache blocks. Using soft updates to track and enforce metadata update dependencies, a file system can safely use delayed writes for almost all file operations. This article describes soft updates, their incorporation into the 4.4BSD fast file system, and the resulting effects on the system. We show that a disk-based file system using soft updates achieves memory-based file system performance while providing stronger integrity and security guarantees than most disk-based file systems. For workloads that frequently perform updates on metadata (such as creating and deleting files), this improves performance by more than a factor of two and up to a factor of 20 when compared to the conventional synchronous write approach and by 4-19% when compared to an aggressive write-ahead logging approach. In addition, soft updates can improve file system availability by relegating crash-recovery assistance (e.g., the fsck utility) to an optional and background role, reducing file system recovery time to less than one second.