Lustre can even pass its checksum to ZFS so the storage system doesn't waste time calculating a new, and presumably unchanged, checksum. So it would seem like an obvious thing to put the two operations together, which is what Bojanic and his team are doing. One of the nifty features of ZFS is that it runs its own checksum to ensure that the disk controller doesn't change data as it is written. If the checksum at the end of the journey matches the one at the start, then the data hasn't changed en route. The most recent version introduced what Bojanic called over-the-wire checksumming, a quick numerical tally done at the beginning and end of a data transmission. For instance, the Energy Department's Lawrence Livermore National Laboratory uses Lustre for its BlueGene/L system.

Six of the top 10 computers in the semiannual Top 500 list of the world's most powerful supercomputers use Lustre, Bojanic said. A client seeking data consults the metadata server for the location and then retrieves the data directly from the appropriate storage server. A metadata server keeps track of all file names, directories, permissions and file layouts. Lustre is widely used in the high-performance computing community because of its ability to pool massive numbers of storage disks into a single file system. 'When you write data to the disk, you know it can be repaired if anything goes wrong,' he said. Advanced data integrity means the system as a whole, rather than its individual components, can guarantee that the data has stayed intact. Bojanic said one of the most interesting opportunities Sun sees for Lustre is that it could be used when used alongside Sun's 128-bit next-generation file system, ZFS, to provide advanced data integrity.

We thought it would be a good time to catch up with the company to find out what's in store for the file system. A year ago, Sun acquired Cluster File Systems Inc., the former maintainer of Lustre. The topic came up while we were talking about the future of the Lustre global file system. In one setup, after a lengthy investigation, the technology staff found that the network cards were flipping bits. 'In some large deployments, we experienced inexplicable data corruption to files on the disk,' he said.

He said that although there are plenty of studies about disk reliability, few have been done on the subject of data reliability on the network ' a problem that is increasing. How did that happen? 'It's staggering the risks that can happen along the entire data path,' said Peter Bojanic, director of Lustre engineering at Sun Microsystems. Yet when the data is read later, it has been corrupted. All the systems involved seem to send the data correctly, and it is written to the disk without any error messages. Ever have this problem? You want to get a large piece of important data from the server to the storage system.

Pool corruption in file area