Novell Inc has finally made its fault-tolerant system, based on a duplicate server system, commercially available – but only to privileged customers. In the first incarnation, Novell mapped out its System Fault Tolerant strategy in the mid-1980s. SFT Levels I and II, which provided re-mapping of bad sectors and complete disk mirroring respectively, followed swiftly, but Level III – dual, mirrored servers, has been hampered by technical considerations and a limited market. After extensive beta testing, SFT III has emerged as a specially re-written version of NetWare 3.11 with a NetWare 4.0 version promised around the middle of next year – six months after the main edition of the network operating system is released. According to Bob Young, director of Novell’s NetWare products division, the company has completely restructured the network operating system. The rebuild divides the system into the parts that make no direct hardware calls and can be mirrored, and those that are intimately linked to the physical server. Young says that there is no particular performance degradation involved in the restructuring, nor is it it noticeably more complex for administrators or users. Most changes, he says, occur during installation. Technically, there is no reason why the SFT III version of NetWare should not, in time, become the standard version, but whether SFT III will ever be folded in as a standard offering, as have SFT I and II, remains a marketing issue. As expected, the two servers are linked via a high speed umbilical link, but instead of having to use an FDDI, the Mirrored Server Link merely defines a driver specification that adaptor manufacturers can choose to support. The mirror link can run at any speed, however, server operation is limited to ensure that the two machines always keep in step. According to Young, it is theoretically possible to use Ethernet as the Mirrored Server Link, but performance would be fairly dreadful. Three companies have initially announced support; Eagle Technology Inc, which builds Novell-boxed local area network adaptor boards, Plaintree Systems Inc and Thomas-Conrad Inc. Eagle’s Netware Mirrored Server Link EISA board delivers an actual data rate of 128Mbps, according to the company, and comes in coaxial and fibre versions.
Mirrored Server Link
The $1,100 copper system enables servers to be up to 100 feet apart. The optical system, which costs $500 more, enables servers to be up to two and a half miles apart. By contrast, Austin, Texas-based Thomas Conrad has written new Mirrored Server Link drivers for its existing, proprietary 100Mbps Thomas-Conrad Networking System adaptors. It is making the drivers available for free download from Compuserve, among other places. Plaintree Systems’ WaveBus adaptor is fibre only, offering maximum distances of 1,500 feet between servers and come in AT, EISA and Micro Channel versions. A kit that includes a pair of boards and 10 yards of fibre costs $3,500. Why choose these particular vendors? Young says that they were self-selecting: when Novell approached various adaptor manufacturers, these were the ones that jumped first. For organisations using NetWare servers as application engines comes the news that well-behaved NetWare Loadable Modules should be mirror-capable. Well-behaved in this context means not writing directly to the hardware, according to Young, who says that SQL modules should function quite happily, taking over immediately if the twin fails. The controlled availability version has a few shortcomings, with both Macintosh and TCP/IP support are missing. This is one reason that, despite extensive beta testing, the product is still not on general release. The other is that the company intends a special degree of support for SFT III customers, and Young says that the company will make sure that we do not over-burden ourselves. In the US, the numbers will be kept down to the hundreds initially, but Young says that the controlled release is definitely temporary. The NetWare 4.0 SFT III product will be out next summer on general release,
but no details on when a full version of NetWare 3.X SFT III will be available. In the UK, NetWare 3.11 SFT – which comes only as a 250-user version, is being sold by Azlan Ltd at UKP12,220. Novell UK reckons that around 50 customers have put their names forward.
