Abstract: A method for controlling access to a storage element that forms a portion of a logical storage device includes setting a write-barrier value to a first value upon receiving a request to copy the contents of the logical storage device. Write operations to the storage element are prohibited with the write-barrier value set to the first value. The portions of the logical storage device associated with the storage element are then copied. Upon the completion of the copying, the write-barrier value is then set to a second value.

Abstract: A file system is distributed over a plurality of computers connected to each other by a network. The plurality of computers execute user programs, and the user programs access files stored on a plurality of physical disks connected to the plurality of computers. The file system includes a plurality of file servers executing on the plurality of computers as a single distributed file server layer. In addition, the file system includes a plurality of disk servers executing on the plurality of computers as a single distributed disk server layer, and a plurality of lock servers executing on the plurality of computers as a single distributed lock server to coordinate the operation of the distributed file and disk server layers so that the user programs can coherently access the files on the plurality of physical disks.