HP Donates the Guts of Tru64 Unix's File System to Linux

Published: June 24, 2008

by Timothy Prickett Morgan

Say what you will about the makers of proprietary minicomputers from days gone by, but Digital, IBM, and Hewlett-Packard all knew a thing or two about making a tightly integrated, highly polished system. And in most cases, that expertise in VMS, OS/400, and MPE infused their respective owners' Unix development projects with a certain amount of finesse. The smarts that went into these proprietary and Unix platforms sure would come in handy as Linux tries to take on more and more of the enterprise.

That's why HP this week is donating the code and documentation behind its Tru64 Unix Advanced File System (AdvFS) to the open source community--and specifically, HP's Open Systems and Linux Organization, which steers the company's cross-divisional open source projects, is saying that the source code and documentation donation is explicitly designed to help the Linux community as it creates the next generation of file systems for the platform.

HP is still patching and updating Tru64 Unix V5.1, and customers using VAXen and AlphaServer iron can still buy that Unix variant because HP says it will be supported at least though 2011, for all intents and purposes Tru64 Unix, its AdvFS file system, and its TruCluster extensions for clustering systems are all dead--but technically elegant and still, for many, useful--products. In the wake of the HP-Compaq merger in the summer of 2001, HP committed to port the AdvFS file system and its TruCluster extensions to the HP-UX 11i v3 operating system. After two years of trying that port, and experiencing other delays with Itanium chips from Intel and its own Unix development efforts, HP decided to spike the AdvFS and TruCluster effort just tell its customers to use the file systems and clustering software from Veritas, which is now owned by Symantec.

According to Bdal Garbee, chief technologist for HP's OSLO unit, there was a lot of good technology inside AdvFS and a lot of the work that was done on the HP-UX port in particular could be useful for ideas as the Linux community mulls its options for the next generation of file systems. And to that end, HP is releasing the source code of the current Tru64 Unix variant of AdvFS and the unfinished development version of the HP-UX port under the GNU GPL v2 open source license--the same license that the Linux kernel and a whole lot of open source software affiliated with Linux is under. The HP-UX port, says Garbee, was "feature complete," but he adds that what might be more useful to the Linux community is all of the internal documentation that comes with the code. This documentation explains the options HP's techies had for a file system and their reasoning of the shortcomings and benefits of various approaches, and then goes into why they made the choices they made in creating and extending AdvFS.

Right now, says Garbee, the Linux community is working on the ext4 kicker to the current ext3 file system that has become the default Linux file system, more or less replacing the more popular ReiserFS. The AdvFS code and smarts is not really going to be all that useful for ext4, which is expected to go into technical preview in the next year or so. But HP thinks that AdvFS will be a big help to the kicker to ext4, called BTRFS, pronounced "ButterFS," which is a file system originally created by Oracle (and not to be confused with the Oracle Cluster File System code that is part of Linux already) and which is becoming the focal point of development for the file system beyond ext4. BTRFS was launched in June 2007, and is a POSIX-compliant file system that will support very large files and volumes (16 exabytes) and a ridiculous number of files (two to the power of 64 files, to be precise). The file system has object-level mirroring and striping, checksums on data and metadata, online file system check, incremental backup and file system mirroring, subvolumes with their own file system roots, writable snapshots, and index and file packing to conserve space, among many other features. BTRFS is not anywhere near primetime, and Garbee figures it will take at least three years to get it out the door.

Given that, and the technology inside Tru64 Unix's AdvFS, now was the perfect time to open the source code and documentation up--and to provide a substantial base of "prior art" legal protection for the BTRFS file system as it is being created.

Now, don't misunderstand what HP has done here. HP has not open source Tru64 Unix or the TruCluster clustering software--just the code for AdvFS, the file system for the old Digital Unix. HP is not trying to establish a project to even port AdvFS to Linux, either. It is just letting people steal as much as they can and put it to good use in BTRFS. The code that HP has released is not ready to be compiled for Tru64 Unix or Linux, since the interfaces between AdvFS and Tru64 Unix are not being open sourced. Someone could reverse engineer AdvFS for Linux, of course. But that's not HP's goal, and it seems unlikely that anyone will do it.

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