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Unix vs. Linux debate dies down as Linux risks diminish

The arguments against Linux -- RAS, capabilities and scalability -- are quieting down as the platform matures and lures more Unix to Linux migrations.

Where are Unix workloads going? Today, Unix workloads are moving to Linux and x86. Unix vs. Linux sticking points -- like administrator availability, application risk, feature set and maintenance costs -- all favor Linux on x86.

"I started out on SunOS in 1993, then moved to Solaris and used it for almost everything -- Web hosting, mail -- everything," recalled Mike Horwath, co-owner of ipHouse, a hosting solutions provider in Minneapolis, who worked at another hosting provider at the time. But around 2002, enthusiasm for Sun hardware started to wane.

"We started noticing that the performance of these servers was lagging behind other systems," Horwath said. "The servers were incredibly stable, but they didn't have the same oomph as x86 systems -- the performance of these RISC systems just hasn't kept up." Thus began a slow and steady march to x86 hardware running Linux.

Linux system hardware and support can also be purchased for a small fraction of an equivalent Unix system. Hardware acquisition and maintenance costs for x86 Linux vs. Unix systems are often on the order of two or three times less expensive, said Dr. Alex Heublein, senior director for solutions and strategy at Red Hat Consulting, and that's not counting software licenses, which are often priced higher on RISC platforms.

Unix administrators also command a much higher salary versus young-gun Linux admins, Horwath said, and are increasingly hard to come by: "They're a dying breed."

Diminishing risks, limitations

In the beginning, migrating away from the stalwart Unix platform was seen as a risky compromise. Over time, those concerns have diminished, experts say.

Initially, x86 and Linux's reliability, availability and serviceability (RAS) features were a huge question mark for administrators coming from the world of bulletproof Unix systems, but those concerns have been mitigated by Linux's increased maturity, plus new availability features found in virtualization software such as VMware. "VMware Fault Tolerance is severely limited [to systems running on a single CPU], but it gives you near 100% uptime," Horwath said.

Grumbling about Unix features that are missing from Linux is also on the wane, said Kerry Kim, director of corporate marketing at SUSE, whose SUSE Linux Enterprise Server is a common destination for Unix-to-Linux migrations. Still, Solaris admins routinely lament the loss of DTrace, ZFS and Solaris Containers.

"People can agree to disagree whether the capabilities in Linux are on par," said Kim, but SUSE has functional equivalents for all those popular Solaris features, including System Tap for tracing, high-performance Btrfs and Linux Containers.

Linux scalability, meanwhile, is now on par with some of the largest scale-up Unix systems. SGI's Linux-based UV 2000, for instance, scales to 4,096 threads on 256 Intel Xeon processors, and up to 64 TB of memory. "That's comparable to an HP Superdome," Kim said.

"The question is no longer 'does Linux scale,' or 'does it have the RAS capabilities of Unix?'" he said. With all the advancements in the Linux kernel and subsystems, "The question is, rather, what is the justification for keeping it on Unix?"

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