News Review: HP bins Compaq clustering
The Clustering Crown passes to Veritas as HP bins Compaq technology.
The announcement by HP recently that they had abandoned the project to port TRU64 clustering to HP-UX was not that surprising, but just very sad for techies like myself who grew up on the old Digital Clustering Technology. It marks the end of an era, and yet another proof, if one were needed, that commercial issues must override technical ones when it comes to running a software company.
Some history...
The Digital Clustering Technology started with VAX/VMS version 4.0, and was a culmination of considerable effort to losely couple VMS systems together. However, this was more than just lose coupling. It involved a fundamental change in the filesystem and kernel of the OS. Every piece of VMS source code had to be re-compiled in order to work with VMS 4.0. I know - I had to do it at the time!
VMS clustering worked because all QIO calls to do I/O to disks devices were intercepted by the "distributed lock manager". This piece of software enabled a user process on one VMS system to take a lock on a resource (say, a file record), and for that lock to be visible to all other machines in the cluster. Every time someone tried to access a file or record, there was a small packet of network traffic required to synchronise the locking with the other machines. The beauty of the system was how elegantly, and efficiently, this traffic was minimised.
The net result of VMS clustering was that you could have multiple machines reading exactly the same disks, files, records or other resources at the same time. At the time, this was nothing short of staggering. If a VMS system crashed (which was very unusual, in my experience), the rest of them simply carried on without interruption. As time went on, it became clear just how advanced this "Share Nothing" clustering feature was. Other manufacturers were unable to meet the challenge
By contrast, most other clustering technologies use a "Share All" approach. In this scenario, Server A takes control of all the disks and resources, leaving Server B sitting idle. In the event of Server A crashing, the application needs to be restarted on B, which takes over ownership of the disks. Compare this with VMS clustering, where there are no idle machines, and all cluster members are fully active all the time.
As if that was not enough, the Digital engineering upped the game even further by working on a similar solution for their own proprietory version of Unix, called TRU64, after Digital was taken over by Compaq. By the time TRU64 version 5.04 was shipping, there were possibities of having shared filesystems, and a genuine Unix "Share Nothing" clustering system.
Why Scrap a good Product ?
We had known for years that this technology was a gold mine. For example, in March 2001 Oracle Licensed Clustering from Compaq which gave the DBMS vendor the technology that eventually led to Oracle 10g.
The basic problem that HP have faced is that this form of advanced clustering required detailed changes to the kernel and the file system. It is, quite simply, too intrusive. If you already have a complex modern OS, the complexity of the changes, not the mention the testing, are almost as much as writing a new OS from scratch
Maybe HP should have standardised on TRU64 when they took over Compaq - but that is another story :-) See the News Story in December 2003 HP have become a profitable company, having successfully swallowed up Compaq.
The Future is Veritas
The Veritas tie-up makes sense to HP, since the HP-UX filesystem was already a derivative of the VXFS Veritas system.
When you take TRU64 clustering out of the equation, Veritas is probably the best clustering technology around for Unix systems.
- Sun Clustering is not very popular. I have heard of Sun salesmen who tell their customers to buy Veritas.
- AIX technology based around HACMP has a reputation with some people of being difficult to configure
- HP ServiceGuard is not a bad solution, but Veritas would be at least as good, in my opinion.
And, of course, Veritas will fight in the Linux market, up against technologies like Convolo, and in the Windows market as well. So Veritas becomes the "Clustering Bus" for your Enterprise - irrespective of Operating System.
Pity I didn't buy shares in Veritas.
Reviewed by Dennis Adams in December 2004