Windows in HA does go
High availability without the rocket scientists
High Availability (HA) environments can obviously be classed as a `good thing’. For most users, however, the balance between need and the cost of implementation usually ends up tipping them towards the `not bother’ side of the fence.
One of the cost issues that plays an inevitable part in this process is that of applications development, for high availability systems have traditionally been specialist environments requiring specialist skills. Put it this way, a typical Windows developer would not be expected to slot into that world at the drop of a hat.
One solution to this, adopted by Marathon Technologies, has been to provide an environment in which Windows developers can become HA `specialists’ without having to learn any new tricks. Indeed, they do not even have to know about development issues for Microsoft’s own clustering environment. According to Marathon’s EMEA sales director, Nick Turnbull, the Windows-based everRun technology makes no demands on developers for it has been developed to appear as a single server. “Any application that can run on a single Windows server can run on Marathon,” he said.
This is due to the architecture of the system and the patented virtualisation technology it employs. The HA software is a virtual server running on one member of a pair of identical servers connected by GBit Ethernet. The single instance of an application then runs in this virtual server, which in turn drives the two servers so that one runs as a permanent hot standby. The virtual server also acts as a metadatabase of the state of the two co-servers to ensure full synchronisation. The virtual server can be switched between the two servers as incidents, or maintenance schedules, demand.
As well as the everRun system, which aims to provide zero downtime continuous availability, there is also a lower-cost implementation called everRun HA. This is aimed at the data replication market and has the added advantage that the servers need not be identical as the virtual server only runs on one of them. There is also a disaster-tolerant implementation called SplitSite.
Though only Windows-based to date, Turnbull indicated that a Linux version is in development. “But users are not running critical applications on Linux,” he rather bravely suggested.
One environment that is a strong base for critical applications is Java and following the rapprochement between Microsoft and Sun Microsytems, and the appearance of news tools to allow Windows applications to run in Java (and vice versa) this could prove to be a useful tool for developers in both camps looking to offer HA operations without recourse to more traditional and expensive options. ®