This paper describes a work-in-progress to design and implement a transactional metadata journal for the Linux ext2fs filesystem. We review the problem of recovering filesystems after a crash, and describe a design intended to increase ext2fs's speed and reliability of crash recovery by adding a transactional journal to the filesystem.

Our Netra NFS group at Sun set out to solve the challenging problem of providing remote Network File System (NFS) service with high performance and availability. An NFS server must guarantee the permanence of changes to the file system before acknowledging an NFS request. Thus, the server’s underlying local file system must perform update operations synchronously to stable storage with potentially high latency. Our solution to this problem involves using the Solaris Unix File System (UFS), derived from the Berkeley Fast File System (FFS), in conjunction with nonvolatile RAM (NVRAM) as fast stable storage. We evaluated the system using the LADDIS benchmark and as a result, developed a cacheing technique for blockmapping information that gav e us a 23 % increase in measured server throughput in our standard RAID-5 server configuration. With recent increases in disk capacity and RAID technology, filesystem sizes have reached a point not imagined by the FFS designers, requiring an approach to checking file-system consistency that does not grow proportionately with file-system size. We examined several log-based solutions to providing fast crash recovery, but none could use the NVRAM effectively and meet our performance requirements. As an alternative, we dev eloped an approach that uses UFS but maintains file-system working-set information, so that the consistency checker needs to examine only the active portions of a file system. This approach met our performance goals and also reduced file-system consistency-checking times to between 3 % and 25 % of those in the original UFS implementation. 1

This paper describes a work-in-progress to design and implement a transactional metadata journal for the Linux ext2fs filesystem. We review the problem of recovering filesystems after a crash, and describe a design intended to increase ext2fs's speed and reliability of crash recovery by adding a transactional journal to the filesystem. Introduction Filesystems are central parts of any modern operating system, and are expected to be both fast and exceedingly reliable. However, problems still occur, and machines can go down unexpectedly, due to hardware, software or power failures. After an unexpected reboot, it may take some time for a system to recover its filesystems to a consistent state. As disk sizes grow, this time can become a serious problem, leaving a system offline for an hour or more as the disk is scanned, checked and repaired. Although disk drives are becoming faster each year, this speed increase is modest compared with their enormous increase in capacity. Unfortunately...