If your looking at different servers to buy for your next virtualization project make sure you check the memory that they come with. New servers utilize DDR3 RAM which comes in several different flavors, there are registered or unbuffered, and single rank, dual rank, or quad ranked…. basically there are a bunch of options.
I’m writing this because most people are just concerned with the number of GB in a server… well your right that makes a difference, but if you don’t pay attention and get UDIMMs you might have to throw them all away and start over with RIMMs at some point.
If you read the small print on the HP quickspec page (and this is true for all Intel 5500 or 5600 series servers as far as I know) you will see that there is a severe capacity limitation with UDIMMs.Maximum (RDIMM) 192GB (12 x 16GB) for Registered Memory configurations
Maximum (UDIMM) 48GB (12 x 4GB) for Unbuffered Memory configurations
In a DL380 or ML350 G6/G7 server there are 18 ram slots, with RIMMs you can only populate 12 of those slots, and the maximum dimm size is 4GB…. hence the 48GB limit.
This isn’t a huge deal if you’re loading windows or linux on the box and it is a standalone server, BUT if your loading VMware or Xenserver and are going to run a pretty decent amount of VM’s that is a problem.
So my recommendation is that if you’re buying new hardware and going to use it for virtualization, make sure your getting RDIMMs and not UDIMMs.