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NetApp's filesystem patents
NetApp (formerly Network Appliance, Inc.) aggressively uses the software patent portfolio they developed while writing their data storage filesystem called WAFL.
 Used against ZFS distributors
 Against Sun and Oracle
In 2007, aka NetApp sued Sun for alleged infringement of their software patents by ZFS. ZFS is a filesystem for storing large amounts of data on computer disks. ZFS is free software, developed by Sun Microsystems.
Oracle's purchase of Sun included the ZFS copyrights and the related patents that Sun was to use against NetApp. However, the risk that Oracle might use these patents against distributors of ZFS are greatly reduced by the patent grant in ZFS's licence, the CDDL.
 Other litigation
In 2010, NetApp threatened companies selling hardware with ZFS installed.
 What about Btrfs?
(Can you help? Is there any reason to think Btrfs is at risk? I don't see any.)
Btrfs is a newer filesystem which shares some goals with ZFS.
 Used to kill tux2
In 2000, the developer of the tux2 filesystem (Daniel Phillips) became aware of NetApp's patents. He developed the relevant techniques four years before NetApp filed for their patents, so he wasn't worried:
I've got prior art; [...] In any event, if they want to argue I think they'll find themselves in a position of having to kiss their main patents bye-bye.
But Phillips gave up on tux2 in 2002. The problem was summarised as:
- It isn't *really* all that similar
- Daniel has prior art going back to the 1980's
- NetApp has more lawyers on staff than Daniel does
 The patent numbers
Three patents are discussed on Sun's (now Oracle's) page on this matter:
- 5,819,292 - purportedly relating to "copy on write"
- 6,857,001 - purportedly relating to "writable snapshots"
- 7,174,352 - purportedly relating to "snapshot"
Phillips' mail about tux2 also mentions 5,819,292 and two others:
- 5,963,962 "Write anywhere file-system layout"
- 6,038,570 "Method for allocating files in a file system integrated with a RAID disk sub-system"
 Related pages on en.swpat.org
- Oracle (having bought Sun) has a timeline that documents the litigation
- NetApp hits Sun with patent-infringement lawsuit, Sep 5th 2007
- ZFS Puts Net App Viability at Risk?, Sun's CEO Jonathan Schwartz expresses regret at having to counter-sue Net App, Oct 24th 2007
- NetApp threatens Coraid over sales of open-source ZFS technology, July 6th 2010
- When Apple dropped ZFS, it was possibly due to patents. Later statements from Sun and Apple referred to the core problem as being "licensing issues", which could refer to patents or to something else.
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