Log-based filesystems often suffer from fragmentation, since each update or write to an existing file causes a new transaction to be created. ETFS uses write-buffering to combine small writes into larger write transactions in an attempt to minimize fragmentation caused by lots of very small transactions. ETFS also monitors the fragmentation level of each file and will do a background defrag operation on files that do become badly fragmented. Note that this background activity will always be preempted by a user data request in order to ensure immediate access to the file being defragmented.