Do-it-yourself X4500 ?

I hate the big discussion forums at IT news sites. They are full of trolls. My favourite trollishness at the moment is the comment “The X4500 is fucking expensive. I can build one of my own for 10 grands”. Okay, let´s talk about this statement. Well, surely you can build one, perhaps much cheaper than Sun. But is it really the same? Or is it only a cheap ripoff of an X4500 that has only the capacity in common. For an outsider the X4500 looks like an normal opteron server with 48 disks. But it starts with the mainboard. It isn´t a standard mainboard. Consider the follwing things:

• In a Thumper all disks are directly coupled onto an disc controller. There are no SATA2-Port extenders in the way. At the end there are 6 seperate SATA2 controllers with 8 SATA-2-Ports each. We´ve used the Marvell 88SX60xx-series for this task.
• The widespread suggestion to use some Areca Cards to mimick an Thumper isn´t an option as well. It´s senseless to plug 24 discs on one controller that uses only one PCI-Bridge with roundabout 1.08 GByte per seond. Only a quick calculation: A Hitachi Deskstar was benched several times with a little bit more than 60 MBytes per Seconds. 24 of this discs results in a datastream a little bit short of 1500 Mbytes per second. So you can get only two thirds of the maximum performance through the PCI-X slots. And this is calculated with the peak max performance of PCI-X. So you have to use at three of this cards. I would even say, you need four or five to have headroom for the next generation high capacity harddrives (perpendicular recording accelerates the drives as well it increases their capacity)
• Now you have a different problem. Find a PCI-X board with 3 logical seperate PCI-X busses. Every configuration sharing busses will see the bottleneck described . So you have to find a bord with two AMD8132 Bridges, something i doubt you find on el-cheapo mainboards.
• The Thumper uses three HT-Channels to directly connect this dics controllers. 16 Ports shares one HT-Channel with 8 GBytes per second, as two Marvell-Chips are coupled to one HT-Channel. 8 discs with 60 MBytes per seconds gives you 480 MByte/s. Well inside your 1.06 GByte/s limit to have some headroom for the future. Two of this 960 MByte/s. Okay, well inside the limit of 8 MBytes/s per HT-Channel.

You should look at this diagram to get an overview of the special design of this board. It´s designed specifically for it´s task:

I havn´t even mentioned RAS-Feature, Lights-out-management, Airflow-Design, Serviceability (eg. changing the CPU-Unit). Before somebody tell me again, that he can build a X4500 for 10 grands, please read the architecture white paper of the X4500. Until then, youshould think twice before making bold statements. And to all customers of such systems: When a competitor shows you a similar system, you should look with care on the internal architecture. Perhaps they will sell you the cheap ripoff.