Tim Burton – Media IT My ramblings covering NLEs / Servers / Storage and the odd bit of photography.

Density – More than just CPUs per 42U rack?

There are many new dense (more than two sockets per RU) solutions out there, however they all fall under one the 3 groups:

• Blade - Multiple (8-32) hotswap servers in one host chassis, sharing power and io via plugin modules
• Multi Motherboard - Two or more servers sharing the same PSU and fans, but with independent io
• Half depth - Reduced form factor servers to allow more in one rack, SGI (Rackable) / Verari / IBM iDataPlex

It occurred to me that while the new designs can cram a lot in rack, they don't necessarily make for a dense data center.  I decided to look at how many sockets we get per floor tile (600x600) using 42U racks.  Taking into account aisles (in a hot aisle - cold aisle config) and switching but not perimeter walkways. For example here is the benchmark using 1U pizza box servers.

1U Conventional Servers

4x 42U racks housing 160 dual socket 'pizza box' server = 320 Sockets

2U in each rack set aside for switching to be fair to the blade and iDataPlex systems

7 Tile Pitch - 4 racks = 14 Tiles

22.86 Sockets per rack tile

Double Servers

Servers such as HP's new Sl2x170z G6 cram two dual socket servers into one 1U package, then dock two of these pairs into a common case so they share one set of PSU and fans.  They fit in standard rack infrastructure therefore the same calculations can apply but with double the sockets!

45.71 Sockets per rack tile

Double Sided Racks

Half depth 1U servers, 320 dual socket servers = 640 Sockets

Again 2U for switches.

Deeper 1200mm racks require a 8 Tile Pitch = 16 Tiles

40.00 Sockets per rack tile

iDataPlex

IBM's new solution where they turn the rack sideways to allow twice the amount of servers in one rack.  They have a neat solution where there are 19" mounts down the sides of the rack for switches and PDUs, this allows all the horizontal slots to be used for servers.  84 dual socket boxes in one rack sounds great, but turning the rack sideways means more aisle space to munch up tile allocation.

Lets do the maths on it:

4x Double Racks housing 336 dual socket boxes = 672 Sockets

5 Tile Pitch (when heat exchanger isn't used) - 4 racks = 20 Tiles

33.60 Sockets per rack tile - Not quite as dense as the 84 server a rack would suggest!

Blade Servers

Fit into the same racks as 1U pizza boxes but all the clever form factor is in the case.

4 Racks = 16 Blade Centers = 512 Sockets

7 Tile Pitch = 14 Tiles

36.57 Sockets per rack tile

BL2x220C - Double Server in 1 Blade

73.14 Sockets per rack tile

It seem's messing with the rack layout as with the iDataPlex really doesn't gain you much once in the data center. IBM would argue that their cooling system is superior to HP's along side water coolers, however it does still add a tile to the pitch as the 'hot' aisle needs to be 1200 instead of 600 when the rear doors are fitted.

HP SL2x170z G6 and the DL2x220c seem to be the clear winners.