The dedupe operation could be on file-level and block-level. The file-level operation checks for the attributes of file against an index. Only the unique files are stored (or backed up) and copies are replaced with a pointer to the original (stub or a subroutine to a program). The block-level dedupe operation goes beyond and creates chunks within a file. Each chunk is then parsed with a hash algorithm such as SHA-1, SHA-2, or, SHA-256. Even a smallest update modifies the hash. The hash is stored against an index. In rare cases, a problem known as hash collision arises. This is a situation where two blocks have produced the same hash. In this case, data loss happens and the situation is termed as false-positive.