Snapshot copy reserve sets a specific percent of the disk space for storing Snapshot copies. If the Snapshot copies exceed the reserve space, they spill into the active file system and this process is called Snapshot spill.
The Snapshot copy reserve must have sufficient space allocated for the Snapshot copies. If the Snapshot copies exceeds the reserve space, you must delete the existing Snapshot copies from the active file system to recover the space, for the use of the file system. You can also modify the percent of disk space that is allotted to Snapshot copies.