Matthew Dillon is starting to commit parts of his HAMMER file system work; he anticipates it being available in beta form by the 2.0 release at the end of this year. He posted a design document, describing how it should work. Some highlights from my reading of it:

• Maximum size: half an exabyte
• Infinite snapshots, limited only by retention policy
• Streaming backups
• Asynchronous transactional support – no long fscks to check disk state

(Someone correct me if I’m summarizing inaccurately.) Some details from the ensuing discussion include comparisons with ZFS, RAID, and backups. KernelTrap also has a nice summary.