Transactional file systems can be fast

Transactions ensure simple and correct handling of concurrency and failures but are often considered too expensive for use in file systems. This paper argues that performance is not a barrier to running transactions. It presents a simple mechanism that substantially lowers the cost of read-only transactions (which constitute the bulk of operations in a file system). The approach is inexpensive: it requires modest additional storage, but storage is cheap. It causes read-only transactions to run slightly in the past, but guarantees that they nevertheless see a consistent state.