Now that VMWare's free VMWare Server product has gone gold, I thought I'd spend some time evaluating it against Microsoft Virtual Server 2005 R2.
I took 2 identically spec'ed boxes (Athlon64 X2 3800+, 2GB RAM, 160Gb SATA2 disk for Virtual disk files and a separate 40GB IDE disk for the host OS), both running Windows Server 2003 R2 x64 Enterprise Edition. The OS was installed on one box, sysprep'd, then imaged onto the other box so they were identical in all aspects. Virtual Server 2005 R2 x64 Enterprise Edition was installed on one, VMWare Server 1.0.0 was installed on the other.
I then built up a little virtual 'branch office' environment, which ultimately consisted of 4 VM's - a DC, an IIS box with SQL Express 2005 + SP1, a file server, and an ISA 2006 RC1 (Standard Edition) box. All running 2003 R2 Enterprise (32bit), with 384Mb RAM and an 8Gb primary disk (single partition). The virtual disks were contiguous files (thanks to contig.exe from sysinternals), and again all copies of a master sysprep'd disk.
Thoughout the process, I took perfmon metrics of the usual CPU, Memory and Physical disk counters, as well as timing a few installs and boot times. I had planned on doing some more testing after the environment was built, but given how close the 2 products ended up being, I'm not going to bother. The only real differentiator was the background chatter of VMWare Server (when the 4 VM's are running idle, there was about 8% CPU utilisation on the host, versus about 0.5% for Virtual Server), which apparently is linked to Windows x64. Hopefully they can do something about that soon.
Of course, there are many, many differences between the 2 products, and each of those differences differs in importance depending on what you're looking to do. Me personally, after running through a base setup and finding bugger all difference, I'm going to stick with running Virtual Server 2005 R2 at home purely because (a) I'm a Windows engineer and the closest to Unix I get is the Red Hat 7.2 & RHEL 3 service consoles of ESX 2.5x and 3.x respectively (both of which run fine in Virtual Server 2005 R2, in fact Red Hat 7.3, RHEL 3 and RHEL 4 are fully supported) and (b) the differencing disks feature.
For those who don't know what differencing disks are, it's kind of like the snapshots feature of VMWare Server however you can run multiple virtual machines from the 1 'master' virtual disk. So for example, I have one 8Gb master Windows Server 2003 R2 virtual disk which is sysprep'd, and then based on that I have about 23 individual VM's (DC's, a few application clusters, IIS, SQL 2000, SQL 2005, LCS, ISA 2004, Terminal Services, Citrix... you get the idea :-) running off that master, each with their own customisations. But instead of needing 23 x 8Gb disks, I actually only need the 1 x 8Gb master disk, and 23 'differencing' disks, which are bascially the changes I have made from the master. Each differencing disk is about 1Gb in size, depending on what is installed. I do things like create separate little 2Gb or 4Gb fixed secondary disks for things like installing databases or IIS onto, so they are off the C: drive (just as should be done in the enterprise).
Not that I can run all 23 at once, but I could if I had a grunty enough box. Now if I wanted to do this on VMWare Server, I'd need 23 x 8Gb files, and I'd be enabling snapshots for the post sysprep stuff on each one, so I'd probably end up with another 23 x 1Gb files as well. So that would be over 200Gb of disk just for that. And then there would be the space required for the nvram files, etc. With Virtual Server 2005, I can do it with just over 30Gb of space plus the nvram files.
But as I said on the VMWare forums, in an enterprise environment, I wouldn't even consider Microsoft Virtual Server, purely because of the lack of a centralised management tool like Virtual Center. The Virtual Server administration website just doesn't cut it (yes I do have it running on a separate machine). For starters, in an enterprise you'd most likely be running ESX anyway, so having the one management tool for ESX and VMWare Server makes a lot of sense.
In a small / medium business or test lab however, if Windows and Red Hat / Suse Linux was all you needed to run, I'd get straight in there with 2003 x64 and Virtual Server 2005 R2 x64.