This year's LinuxWorld Conference & Expo boasted a whole new crop of clustering products. Commercial clustering solutions are finally ready for harvest. No longer are we stuck in a relative wilderness of Beowulf-only clustering -- the focus of attention for most academic institutions and scientific applications. Now, high-availability, load-balancing opportunities prance about in gleeful attempts to attract the most customers.

It is great to see a wide range of products focused on clustering finally emerge in commercially supported systems. This legitimizes the product, since companies that once hesitated because of the lack of available support can now confidently accept Linux-based clusters from small and large vendors alike.

The show's events took place both on the exhibition floor and in the session presentations. The exhibits were mostly manned by salespeople, but I was able to find technical staff and product managers to explain their products in detail, free of sales-speak.

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I witnessed Mission Critical Linux's working demonstration of its tightly coupled high-availability Convolvo Cluster system for pairs of Linux nodes. The two systems are connected by a private 100BaseT Ethernet with a crossover cable, as well as a direct null-modem serial cable. They attach to the same storage system through standard SCSI cables, allowing either to issue disk commands. This requires a SCSI storage system with a dual-attachment feature, which raises the cost. Mission Critical also offers special intelligent power supplies for each node, with cross-connected controls between nodes so a failed node can be hard-rebooted by the working node.

The nodes need not be identical, as long as they communicate with each other and the SCSI channel at approximately equal speeds, and run the same Linux distribution, along with any system changes. Mission Critical has not published numbers for actual failover response times. The nodes work by maintaining a quorum partition on the attached storage system. Through this partition, they can also exchange data -- such as which node will run a specific application, and which applications should failover to the other node.

The system is managed by a command-line interface or a Web-based GUI that can execute all the functions needed to operate the cluster. When a node fails, the cluster executes an application failover script to restart the application. While several major applications, like Apache and Samba, have been implemented on Convolvo clusters, no published API will allow software developers to incorporate direct failover within their applications. The software costs about $995 per node, or $1,990 per cluster pair.

Alongside their current multinode clustering on PIIIs and Xeons, SGI demonstrated an impressive eight-node clustering of IA-64 systems from their 1200, 1400, and 1450 Linux server lines. SGI's real contribution to Linux is

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