PVFS: A Parallel Virtual File System for Linux Clusters
As mentioned before, PVFS does not implement many security features at this time. It is primarily intended for use on private cluster networks that can insure trusted clients. There is no restriction on client connections, nor is there any encryption or keys used to verify user authenticity. Client nodes are generally trusted to provide accurate UID information for use in file permissions and ownership checks, just as in NFS.
There are many changes and advances in store for PVFS. The existing generation of PVFS is undergoing modifications and testing to support a higher degree of scalability. These mostly address issues with supporting large numbers of TCP/IP sockets. They will also resolve the issues inherent in supporting 64-bit (greater than two-gigabyte) file sizes and offsets. This will allow PVFS to scale to the current size of large-scale clusters that utilize hundreds or thousands of nodes.
PVFS as a whole is undergoing a full redesign at the same time. This will result in a complete rewrite of PVFS that incorporates new technology and lessons learned from the previous implementation. This version of PVFS will not be available for quite some time but is already in active development.
Some of the features that will be supported in the next generation are:
Reactive scheduling that allows PVFS to adapt policies based on system state and application load
Modular support for a variety of networking systems, so that the file system is no longer bound to TCP/IP but can take advantage of more advanced messaging protocols as they become available
Modular support for a variety of storage methods to allow I/O dæmons to access local data through various methods, such as raw I/O or asynchronous I/O
Multiple manager support
Redundancy of both I/O data and metadata in case of system failure
Improvements in the UNIX compatibility layer
More advanced options for data distribution as well as data representation
After evaluating several distributed file systems, we chose to use PVFS for applications that require intensive I/O. PVFS, in its current state, does not provide any redundancy or high security features. However, the research is still ongoing, and we have high hopes in this regard. We believe that if PVFS were to provide access security, data redundancy and management node redundancy, then it would be more suitable for adoption as part of a highly scalable, reliable and fault-tolerant Linux cluster. As it stands now, however, it is more suited for application domains (such as scientific computing) in which optimal performance is paramount rather than high availability.
I had a pleasant experience with PVFS and with the developers who provided a lot of help as we achieved the above setup and contributed much to the writing of this article.
If you are interested in distributed file systems and you need support for high-performance I/O, I highly recommend that you try out PVFS. PVFS is freely available under the GPL and can be downloaded from Clemson University's web site (see Resources).
Primary PVFS developers: Robert Ross, Mathematics and Computer Science Division, Argonne National Lab. Philip Carns and Walt Ligon, Parallel Architecture Research Lab, Clemson University, with support from NASA's Goddard Space Flight Center as well as Argonne National Lab. Ericsson Research Canada: The Systems Research Department at Ericsson Research Canada for providing the facilities and equipment as well as approving the publication of this article.
Philip Carns (firstname.lastname@example.org) is a graduate student at the Parallel Architecture Research Lab at Clemson University. Robert Ross (email@example.com) is employed at the Argonne National Laboratory by the Mathematics and Computer Science Division. He will receive his Doctoral degree in Computer Engineering from Clemson University in December 2000.
Ibrahim F. Haddad (firstname.lastname@example.org) works for Ericsson Research Canada in the Systems Research Division. He is currently a DrSc candidate in Computer Science at Concordia University in Montréal.
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