Citrix has put out XenServer 4.1, the first rev of the open source virtualization software since it bought XenSource late last year.

Along with the dot release Citrix has simplified its pricing model to let customers deploy an unlimited number of virtual machines or guest operating systems for $600 per server a year or $900 per server perpetually, adding to the virtualization price war against VMware that Microsoft started.

The pricing, different from the usual per-socket licenses that Citrix claims jacks up the overall cost of virtualization and adds customer-annoying tracking requirements, applies to all editions of XenServer, including the coming new Platinum Edition due out this month, which dynamically provisions both physical and virtual server.

The Citrix pricing is good for servers with up to four CPU sockets.

VMware – as will Microsoft when it gets here this summer – charges per processor.

A free Express Edition is still available for use on a single server.

Citrix claims the number of resellers trained to sell XenSource has jumped from 300 to 2,500 since October and the unspecified customer base has doubled. It also claims that OEM agreements with Dell, HP, Lenovo and NEC have embedded it “on more than 50% of all 64-bit x86 server sold worldwide.”

Meanwhile, it’s cut a deal with NetApp that delivers a server virtualization scheme that embraces NetApp’s storage.

It means using a jointly developed Adapter for NetApp ONTAP that manages storage configuration and provisioning from a single console.

All on ONTAP features can be accessed from the console and is supposed to simplify the use of virtual servers in NetApp networked storage environments.

The stuff’s bundled in XenSource 4.1 and can be used for thin provisioning og virtual disk images (VDIs), VDI cloning and snapshots.