Unionfs recursively merges several underlying directories or branches into a single virtual view. The efficient fan-out structure of Unionfs makes it suitable for many applications. Unionfs can be used to provide merged distribution ISOs, a single /home namespace and more. Unionfs' copy-on-write semantics make it useful for source code version-ing, snapshotting and patching CD-ROMs. We benchmarked Unionfs' performance under Linux 2.4. For a compile benchmark with one to four branches, Unionfs overhead is only 1-2%. For an I/O intensive workload, the overhead ranges from 10% for a single branch to 12% for four branches.
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