> dell m905 ... 100$

These are really old, Socket F, DDR2 blades. Given that the corresponding blade center will be needed as well, probably not that good a deal.

Alright, and what about more recent blades around 500$ ?

I considered blades but at least for me I concluded they were a bad fit:

- The centers are large and heavy, needs a fair amount of space, can't really be handled alone. Also means they're shipped on a pallet, which is somewhat expensive.

- Blades are less common overall compared to servers

- Blades have more peculiar I/O than normal servers, you can't just stick an IB card or GPU in there

- The backend I/O modules are fairly rare 2nd hand, so either you find a center which has the modules you want or you're SOL

I have both HP g6 blades and Dell C6100 blades at home...you can get both for about $200/node with 2xquad core and 24G of Ram. The only real issues with them are the NOISE and the electric usage. 16 nodes sounds like your living in an airport. The HP is 8 nodes with a shipping weight of 300 pounds. Cost $350 for shipping, IIRC - pop the sleds and the heaviest part is probably ~25 pounds, easy to handle without help. The HP blades also came with mellonox 10G cards.

How difficult would be to add liquid cooling ?

With a drill and duct tape, it can be done

and a drop of anti freeze

Fair points

Per https://news.ycombinator.com/item?id=13607257 ~3 months ago:

I'd start with a used Dell Precision T7xxx series off of Ebay for a <$300 including RAM and a Xeon or two

T7500 are above 500$ with 24GB of RAM, T7600 are quickly above 1000$. Not expensive but not a sub 100$ pizza box.

Thanks for the tip though, could be of use for a friend.

T7500 with 48GB RAM is $300 + shipping on ebay: http://www.ebay.com/itm/Dell-T7500-Home-PC-Xeon-6-Core-3-06G...

As a side note to your side node, rpi clusters are a terrible idea in any case :-)