Sequent Computer Systems Inc has added a couple of key technologies to its clustering and Fibre Channel I/O strategies with the inclusion of a cluster file system in its Dynix/ptx Unix operating system and the integration of a fibre channel switch its NUMA-Q servers. The cluster file system, a concept pioneered by DEC in its VMS operating system, includes a locking mechanism that provides multiple nodes in a cluster, each running an instance of the operating system, with shared access to the same file without compromising the integrity of the file or its contents. The major Unix server vendors are still some way behind Sequent in being able to ship clustered file systems, which enable developers to write their own cluster-enabled applications which can access files across high-speed FC interconnects. Most vendors still require NFS network file system implementations to share files across a network. Sequent, which has still to announce a source to meet its future 64-bit Unix requirement, says it supposes the file system would work just under Solaris x86 or other 64-bit APIs.
Sequent says it is also shipping Brocade Communications Corp’s SilkWorm 100 megabyte per second Fibre Channel switch integrated with its Intel-based NUMA-Q 2000 SMP Unix servers. The net effect is that SilkWorm provides multiple access paths from processor to disk rather than the one or two links provided by other Fibre Channel configurations such as FC-AL Arbitrated Loop topologies. Up to two FC-AL loops, each with 126 devices, can be connected to an I/O slot but an integrated FC switch offers multiple simultaneous access points and the ability to create a mesh or fabric of many FC connections between devices. In addition an FC- AL hub is a sheer bandwidth mechanism which divides up the 100Mbps between the attached devices. If one device along the connection fails the whole loop goes down and because the Class 3 fibre channel protocol techniques FC-AL uses don’t require a comprehensive checking of the network before data is sent to a device the combination is characterized by the enterprise crowd as spray and pray. FC use highly-managed Class 2 fibre channel protocols. Sequent believes FC switches are essential in high- availability, mission-critical and enterprise data environments in the terabyte range and up, although it’s priced a six-port version of the Brocade switch at only 20% (offering three times the bandwidth) of an FC-AL hub to make it cost effective for users with 100Gb of data and up. The downside is that FC fabrics requires more complex software than FC-AL loops and is more difficult to implement. To utilize FC switches, the software must know the addresses of every device. Sequent’s first pass at the FC technology using the Ancor Communications Inc switch came to naught (CI No 3,198), because of technical problems. Sequent says the switch was available to half of its third quarter NUMA-Q server ships and will hit 95% coverage this quarter as it replaces FC-AL, although it will continue to sell point-to-point and FC-AL fibre channel solutions where required. It’s going to start selling the eight-way NCR Corp OctaScale servers shortly.
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