what rack size do I need for xserve?

You need one or more racks that are taller in aggregate than the sum of U units you want to rack-mount (both for your immediate plans, and for your plans going forward for a reasonable time going into the future), and deeper in depth than the deepest widget you plan to mount, and physically able to fit where you plan to use the racks (including through doorways and hallways and stairways and elevators), and appropriately quiet for the target environment if it's not a dedicated computer room or server closet.

"Standard" racks are generally 19" wide between mounting rails, with square or round holes in the front rail. Square holes are used for captive mounting nuts. Round holes for racks that don't use the captive or caged nuts.

Beyond the 19" width and the vertical spacing of the holes, there is great variability.

Some environments use underfloor cooling to feed cool air into the rack, others use rackmount fans or even rack-side cooling units. Some environments use partially-open racks or rail-mounting frames, and room air conditioning, sometimes supplemented with rack-top fans. Some have acoustical insulation; an Xserve isn't loud as servers go, but it's more than most folks want in an office. Different racks have different capacity limits.

And in general, poorly-built (and often cheap) racks aren't worth it. They rack (twist), they're hard to disassemble, components bind, and they tend not to fit anything right. (I'm not implying anything here about the racks you cited; I'm not familiar with that series. )

The US Apple store offers Gizmac acoustical racks for use in office environments. There's the XRackPro2 25U option, for instance. There are (many) racks and (many) options (eg: rack-mount keyboard and LCD drawers), and many, many rack styles.

The Xserve rack-mount kit is among the most flexible I've encountered, so long as your rack depth and mounting are within its rather generous limits. It's usually mounting the other stuff (switches, storage arrays, less-interruptible power supplies (LIPS; often erroneously referred to as UPS or as "uninterruptible", etc) into the rack that seems to leave me peeved.

When we bought our 2nd Xserve earlier this year, we needed a rack to fit the old one and the new one. What we bought looks like the picture at the top of the page you linked to. (It's not the same model or manufacturer, but it's the same type of rack).

The dimension of our rack is 100cm (height) x 80 cm (depth) x 60 cm (width). These are the external measures. Internally, the rack fits equipment 19" in width as expected, and the depth is adjustable within the external depth of 80cm. That is, you can disassemble parts of the rack and move them back and forth.

The current Xserve model is 76,5 cm deep. I had to remove the front and back door of our rack, because with them in place they could not be closed. It doesn't matter to us, though. But maybe a rack 90cm deep would have been better. There is equipment like power distribution units that you're supposed to install in the back of the cabinet that you might want to leave some space for. And we can't fit that now in our cabinet.

The current Xserve comes with rails that you install first in the rack, and then you can just slide the entire Xserve in. Very easy to install, and the rails are very flexible when it comes to fitting the Xserve to the depth of your cabinet.

But not all equipment will be as easy to install as the current Xserve. The old Xserve G5 was more difficult, as it comes with several different extenders which you use to install it in the rack. One extender was too short for our rack, and the other one was too long, so even though the new Xserve fitted great we had to disassemble the rack and adjust the depth to accommodate the Xserve G5.

Audun