Enhancements to the Fast Filesystem to Support Multi-Terabyte Storage Systems

This paper describes a new version of the fast filesystem, UFS2, designed to run on multi-terabyte storage systems. It gives the motivation behind coming up with a new on-disk format rather than trying to continue enhancing the existing fast-filesystem format. It describes the new features and capabilities in UFS2 including extended attributes, new and higher resolution time stamps, dynamically allocated inodes, and an expanded boot block area. It also describes the features and capabilities that were considered but rejected giving the reasons for their rejection. Next it covers changes that were made to the soft update code to support the new capabilities and to enable it to work more smoothly with existing filesystems. The paper covers enhancements made to support live dumps and changes made to filesystem snapshots needed to avoid deadlocks and to enable them to work efficiently with multi-terabyte filesystems. Similarly, it describes changes that needed to be made to the filesystem check program to work with large filesystems. The paper gives some comments about performance, and decribes areas for future work including an extent-based allocation mechanism and indexed directory structures. The paper concludes with current status and availability of UFS2.