Apple

Sooo... I've got my hands on two shiny Xserves.

One Xserve 3,1 and one Xserve 1,1 - obviously the Xeon 5500-based gem is the one I'd actually use. (The other one is probably up for grabs)

Since it got a single-CPU configuration, it only has 6 DIMM-sockets, so I'm limited to 24GB (or 48GB if I use 8GB-modules).
I was thinking of running vSphere 5.1 on it and actually install OSX on a VM, which is fully supported in this configuration. Feels somewhat limited in its original OSX Server costume, considering the hardware. OSX isn't (in my mind) enough client-server oriented that I'd use it purely as an OSX Server.

From what I can see it swallows 4GB UDIMM-modules, but up to 8GB RDIMM-modules (which of course can't be mixed) to a maximum of 48GB which is what the board can handle. It uses PC3-8500 modules, but from what I can see it should be able to use PC3-10600 modules with a lower frequency... IF that's the case, I'll probably have an easier time to score some HP-branded sticks since they seem to float up everywhere.

Thoughts?

Anyone dealt with such a beast?
From what I've read they share chipsets, cpu and memory with certain Mac Pro models.

They do, but that's about all I know about the Intel Xserves. I really only worked with the PPC ones.

So that's where your O350s went.

I have a Mac Pro 2,1, which has some similarities to your Xserve 1,1: I'm very happy with the MP 2,1, with eight 3GHz core and 32GB of memory it more than fills my needs for photo editing/management. No experience with vSphere - I run OS X 10.7 (the last officially support OS X release for the MP 2.1), but I the system is set up to dual-boot W7 (via BootCamp) and I also run W7 and Linux as VMs (using VMWare Fusion).

The MP 2,1 and your Xs 1,1 both can hold up to eight 4GB 667Mhz PC-5300 FB-DIMMs, for a total of 32GB. If you need the stuff with Apple-approved heat sinks, the going price for 32GB is likely to hurt your feelings .

In spite of the loss of cooling surface provided by the Apple-approved FB-DIMMs, I've found it is possible to run non-apple FB-DIMMs. Not sure about the Xserve, but by default the fans in the MP run at very low speeds. That probably works well with in an as-sold config, but since I was working with a fairly max'd system, I opted to increase the minimum fan speeds from the default 600 RPM range to 1200 RPM (I'm using Temperature Monitor to monitor the MP's temperature sensors, and smcFanControl to adjust fan speeds. Apple-approved FB-DIMMs in 512MB sizes can usually be had cheaply, so you could also pick up some of those and move the apple-approved heat sinks onto the non-apple memory.

With the tweaked fan speeds it's been running 24/7 for a couple of months with 32GB of not-approved-by-apple memory. With a little patience I was able to acquire the 24GB/six 4GB FB-DIMMs needed to bring my MP up to 32GB (it came to me with two 4GB FB-DIMMs already in place) - for a less than the going rate for 8GB (one pair) of the the apple-approved FB-DIMMs . If you decide to keep it, I think the Xserve 1,1 should make a more than capable server

Funny enough, the Xserve 1,1 uses JEDEC-standard DIMMs , something which seems prohibited in your Mac Pro system.

Considering the size and the amount of heated components inside, I must say it's a fairly silent 1U server after all.
I work as an IT-Consultant and deal alot with HP Proliant based Intel systems, whereas 1U servers *always* tend to emit loud screeming noises, just because of cooling requirements. The Woodcrest based HP Proliants would be equal to Generation 5 (G5) units for comparence and I know that neither of the G5-models is anywhere near silent. There's just too much heat coming from both CPUs and the FB-DIMMs.

The other Xserve 3,1 is Nehalem-based and from what I know they would be equal to HP Proliant G6-series. I haven't dealt much with those generations, but I know the later G7-models are damn near whisper quiet, for beeing servers. Also I believe power consumption is considered much lower on the Nehalem (and newer) generation CPUs.
Nehalem (and newer) uses DDR3 memory which doesn't even require heatspreaders, something that also indicate lower power requirements = less heat.

Talk about jumping to conclusions.

No, really. My boss (who owns a sidekick Mac-hosting company) had these two taken out of service since he replaced them with newer mini's. He upright gave them to me, with the option that I sell one of them for him. I have a kind boss.

I'm right about to install Mountain Lion but was wondering about the "Server version" mentioned in the Xserve User Guide. From what I know there isn't such thing called a special server version of OSX anymore, just an app you buy from Mac App Store, right? Is this still current with the Xserve?

Yep.

But I don't care much for OS X as a server platform; it's never been shockingly performant. Why not ye old Linux?

from what i've heard the 10.8 server addon is a pita

I did install the server addon and it was no pita, really... next, next, finish. In that order.
Now what on earth I would need a Wiki server for or much of the other stuff is beyond me, but atleast I can manage the Xserve more decent through remote tools and use it for Time Machine backups.

I don't know why but for some reason when I try to track down HDD trays (or "Apple Drive Modules") some sellers indicate that the particular SATA tray fits "G5 Xserver and Intel, not Intel 2009").
What on earth is the difference?

Has anyone else seen any difference in the HDD trays?

For reference, I've been running a MacPro 3,1 with 4 non-Apple 800MHz FB-DIMMs for a couple months with no issues heat-wise. Just flat heat spreaders, nothing like the fancy fin arrangements Apple mandated.