An Incremental File System Consistency Checker for Block-Level CDP Systems
An Incremental File System Consistency Checker for Block-Level CDP Systems
复制标题
块级 CDP 系统的增量文件系统一致性检查器
DOI：
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发表时间：
2008
期刊：
影响因子：
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通讯作者：
Shibiao Lin
中科院分区：
文献类型：
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作者：
Maohua Lu;T. Chiueh;Shibiao Lin
块级连续数据保护(CDP)系统记录从应用服务器(例如，文件或DBMS服务器)到存储系统的每个磁盘块更新，使得在时间窗口内的任何磁盘更新都是可撤销的，从而能够提供比传统周期性数据备份系统更灵活和更高效的数据保护服务。遗憾的是，现有的块级CDP系统都不能支持保证与应用程序服务器的元数据一致的任意时间点快照。从数据保护的应用服务器的角度来看，这一缺陷严重限制了数据块级CDP系统在恢复点目标(RTO)方面的灵活性。本文描述了一种增量文件系统检查机制(IFSCK)，该机制旨在解决文件服务器的这一缺陷，并利用文件系统特定的知识来快速修复任意时间点的块级快照，使其与文件系统元数据保持一致。从完全运行的iFSCK原型进行的性能测量表明，iFSCK可以在不到1秒的时间内将10 GB的时间点数据块级快照转换为文件系统一致性，并且在放宽元数据一致性要求的情况下，所需时间不到普通ext3的Fsck实用程序的25%。
A block-level continuous data protection (CDP) system logs every disk block update from an application server (e.g., a file or DBMS server) to a storage system so that any disk updates within a time window are undoable, and thus is able to provide a more flexible and efficient data protection service than conventional periodic data backup systems. Unfortunately, no existing block-level CDP systems can support arbitrary point-in-time snapshots that are guaranteed to be consistent with respect to the metadata of the application server. This deficiency seriously limits the flexibility in recovery point objective (RTO) of block-level CDP systems from the standpoint of the application servers whose data they protect. This paper describes an incremental file system check mechanism (iFSCK) that is designed to address this deficiency for file servers, and exploits file system-specific knowledge to quickly fix an arbitrary point-in-time block-level snapshot so that it is consistent with respect to file system metadata. Performance measurements taken from a fully operational iFSCK prototype show that iFSCK can turn a 10 GB point-in-time block-level snapshot to be file-system consistent in less than 1 second, and takes less than 25% of the time required by the Fsck utility for vanilla ext3 under relaxed metadata consistency requirements.