Mainstream Linux distributions for servers have caught up substantially with Unix in terms of reliability over the past year, while Windows Server 2003 downtime has risen by nearly 25 percent, according to a Yankee Group survey.
The research firm's survey also noted a significant rise in enterprise interest in Ubuntu, previously known primarily as a desktop operating system.
The 2007-2008 Global Server Operating System Reliability Survey presents a substantially different picture compared to the results of the last such survey in 2006, in which Windows administrators reported less downtime than their counterparts who used Linux--a result that stirred up controversy at the time.
Over 2007 and 2008, Linux distributions from Red Hat and Novell increased reliability by an average of 75 percent, respondents to the survey said.
Downtime on Windows Server 2003, meanwhile, increased by 25 percent, to nearly nine hours per server, per year, the survey found.
"Windows Server 2003's decreased reliability is attributable to a series of security alerts that Microsoft issued in the summer and fall timeframe which caused network administrators to take their Windows Server 2003 machines offline for significantly longer periods of time to apply remedial patches," said Yankee Group analyst Laura DiDio in a research note.
The 2006 survey found that both Linux and Windows Server 2003 were relatively crash-prone compared to Unix, but that the Linux systems surveyed have now closed the gap slightly.
Unix systems, which represented about 10 percent of the installed base covered by the survey, still achieved the highest reliability figures. IBM's AIX came highest, with enterprises reporting an average of 36 minutes of downtime per server over a 12-month period. HP-UX version 11.1 recorded 1.1 hours of downtime, while Sun Solaris users reported 1.4 hours per server, per year.
Novell's Suse Linux implementations saw downtime decline by 73 percent, from about four hours in the 2006 survey to just over one hour per server, per year, in the latest survey.
At the same time, Suse's market share rose from 13 percent in 2006 to 17 percent, according to the latest poll.
Downtime for Red Hat's standard, off-the-shelf Red Hat Enterprise Linux (RHEL) distribution declined by 75 percent, from 7.1 hours to 1.75 hours per server, per year. Custom implementations fared better, recording 52 minutes of downtime per server, per year.
Market share for off-the-shelf RHEL rose from 26 percent in 2006 to 31 percent among respondents to the survey .
Debian servers recorded just over five hours of downtime, a decrease of 41 percent from the previous figure.
Twenty-four percent of respondents said they had at least one Debian server on the network, compared to 15 percent in the previous survey, indicating that Debian is seeing increased enterprise usage.
Ubuntu, which has only relatively recently begun focusing on server customers, appeared in the survey for the first time, with 22 percent of respondents saying they had at least one Ubuntu server on the network. Users reported 1.1 hour of downtime per server, per year.
The results are based on an online survey of 700 users from 27 countries. Yankee Group said it used intrusion-detection and authentication mechanisms to ensure accuracy.