After several years of struggling, Sun is gaining ground in the Unix market, according to a new survey.

Gabriel Consulting Group his week released the results of its Unix Vendor Preference Survey, which queried more than 275 enterprise customers about their experiences with and perceptions of the various Unix vendors. Sun lagged in a distant third place last year behind IBM and HP, but the server maker made strides in 2006 and ended up in second place, not far behind IBM.

“This marks a sea change since our last survey,” Dan Olds, GCG principal analyst and CEO, writes in the report. “To Sun’s credit, they’ve done a lot of things right in the last year – successfully introducing their T1000/T2000 multicore Sparc servers, recapturing the Unix revenue crown for the first time in years, sustaining their lead in Unix server shipments, and (finally!) proving they can significantly increase server revenue.”

GCG surveyed data center personnel, such as data center managers and systems architects, rather than CIOs. Its questions centered on topics from technology and performance to service and support. Among the respondents, nearly a third manage more than 50 Unix servers, with most managing 25 to 50. More than three-quarters of the respondents manage Unix systems from at least two of the vendors.

The survey questions were grouped into three areas: technology criteria (system performance, scalability and availability); vendor criteria (QoS and sales organizations, sticking to road maps, and track record on meeting promises); and futures (in which respondents predicted the market landscape for the years ahead).

In the last area, nearly 43% said they expected IBM to be the dominant Unix vendor in 2011, with 34% choosing Sun and 24% betting on HP.

According to overall responses, IBM is the most popular Unix vendor, taking the top spot in most categories. The survey was conducted in October and November when the HP boardroom scandal was at its height, which may explain HP’s low marks, Olds says.