1. A non-transitory computer-readable storage device storing computer-executable instructions that when executed by a computer cause the computer to perform a method, the method comprising: accessing a file system comprising a set of files and metadata concerning members of the set of files, where the metadata includes a set of inodes; accessing a copy on write data store; in a single traversal of a data structure that organizes the file system, identifying an error to be repaired in the file system, where the single traversal of the data structure that organizes the file system is performed while the file system is in a read-write mode, where the single traversal of the data structure includes visiting a member of the set of inodes at most once or visiting a member of the set of files at most once; during the single traversal, writing a repair data to the copy on write data store, where the repair data comprises information concerning a fix for the error, where the information concerning a fix for the error includes a replacement file system block, a replacement file system inode, data from which a file system block can be repaired, or data from which an inode can be repaired; during the single traversal as the file system continues operations, attempting to satisfy a read intended for the file system using repair data associated with a target of the read by redirecting the read to the copy on write data store, where the repair data is stored in the copy on write data store; upon determining that the read intended for the file system cannot be satisfied using the copy on write data store: attempting to satisfy the read from the file system; and selectively updating the file system using the repair data stored in the copy on write data store, where selectively updating the file system with the repair data stored in the copy on write data store comprises providing the repair data to a copy on write process or service, and applying a portion of the repair data provided to the copy on write process or service to fix the file system in response to receiving a signal from a user before the single traversal has completed, where the portion of the repair data includes less than all the repair data.