Importance

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Abstract

A method and apparatus for removing duplicated data in a file system utilizing copy-on-write storage tiers. A synthetic namespace is created via file virtualization, and is comprised of one or more file systems. Deduplication is applied at the namespace level and on all of the file systems comprising the synthetic namespace. A set of storage policies selects a set of files from the namespace that become the candidates for deduplication. The entire chosen set is migrated to a Copy-On-Write (COW) storage tier. This Copy-On-Write storage tier may be a virtual storage tier that resides within another physical storage tier (such as tier-1 or tier-2 storage). Each file stored in a Copy-On-Write storage tier is deduped, regardless of whether there is any file with identical contents in the set or in the COW storage tier. After deduplication, the deduped file becomes a sparse file where all the files storage space is reclaimed while all the file's attributes, including size, remain. A copy of each file that is deduped is left as a mirror copy and is stored in a mirror server. If two mirror copies have identical contents, only one mirror copy will be stored in the mirror server. Read access to a file in the COW storage tier (COW file) is redirected to its mirror copy if the file is deduped. When the first write to a COW file is received, the mirror copy stored in the mirror server is copied as the contents of the COW file, and the association from the COW file to its mirror copy is discarded. Thereafter, access to the “un-deduped” file will resume normally from the COW file.

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First Claim