File clones

SnapshotIQ enables you to create file clones that share blocks with existing files in order to save space on the cluster. A file clone usually consumes less space and takes less time to create than a file copy. Although you can clone files from snapshots, clones are primarily used internally by OneFS.

The blocks that are shared between a clone and cloned file are contained in a hidden file called a shadow store. Immediately after a clone is created, all data originally contained in the cloned file is transferred to a shadow store. Because both files reference all blocks from the shadow store, the two files consume no more space than the original file; the clone does not take up any additional space on the cluster. However, if the cloned file or clone is modified, the file and clone will share only blocks that are common to both of them, and the modified, unshared blocks will occupy additional space on the cluster.

Over time, the shared blocks contained in the shadow store might become useless if neither the file nor clone references the blocks. The cluster routinely deletes blocks that are no longer needed. You can force the cluster to delete unused blocks at any time by running the ShadowStoreDelete job.

Clones cannot contain alternate data streams (ADS). If you clone a file that contains alternate data streams, the clone will not contain the alternate data streams.