HP’s ML115 G5 server has been a popular choice for ESXi lab use because of its quad-core processor and 8GB RAM capacity, but more importantly its fantastic price – often under £200 (although stock is now pretty thin, since the arrival of the G6 models).  The only downside is its low-efficiency but reliable power supply, HP quoting 65%.  Although not a problem for a box fired up for specific testing, when run like mine 24×7 with a full compliment of hard drives and hardware RAID, the ML115′s idle power consumption of over 140W proved a little costly.

Corsair 400CX

There are plenty of 80+ PSUs on the market to choose from, but the Corsair 400CX caught my eye as low cost but with seemingly high quality and continuously rated internals.  With an 80% unit, the consumption of my box should go down to about 114W, saving 26W (£22 a year at 10p/kWhr), paying for itself in two years and saving the equivalent of 1,200 miles of CO2 in my car.

Fitting an ATX PSU to the ML115 G5

The HP standard unit isn’t quite standard ATX size, but even so I thought the switch was worth a go.  As the mounting holes aren’t standard, fitting the Corsair unit means drilling at least one new hole (circled below).  The chasis of the ML115 is very ‘flakey’ when drilled, so great care is required to shield the internals from swarf (and vaccum the unit extremely thoroughly afterwards).

With the mounting hole sorted, the Corsair fits but leaves a gap at the top.  This might result in some hot air recirculation, upseting the overall front-to-back cooling, but also leaves a gap in the carefully designed Faraday cage construction to protect against EMI.  In an effort to alleviate both these problems, a strip of 50mm foil tape (as used for joining insulation boards in house construction) can simply be stuck across the gap.

The cables on the Corsair are pretty long, so some care is needed to roll them all up out the way to avoid creating any restriction to air flow through the server than necessary.  If the top 5.25″ bay is free, the cables can be wrapped up there.  Here it is fitted:

In Summary

The Corsair 400CX is cheap yet efficient with high quality internals and plenty of connectors.  Efficiency wise, the HP and the Corsair PSUs seem to perform exactly to their respective 65% and 80% ratings, and the ML115′s idle power consumption was reduced exactly in line with expectations by fitting the Corsair unit.  Thanks to a large fan there is very little noise from the it, the HP CPU and case fans providing the sound track.

A slight increase in continuously rated power reserve and a three-year warantee should make for reliable power supply that in a well loaded machine can easily pay for itself over its useful life.  I’ve been running this PSU for four months so far without any issues to report, the ML115 continuing to provide the rock-solid stability I’ve come to expect.

About the ML115

The ML115 and it’s Intel based sister the ML110 are compact, easily transportable and yet reliable machines at a complete bargain price.  They both run ESXi 3.5 and 4 without a fuss and will boot from an internal flash drive, making them ideal for virtualisation test beds and home labs.  TechHead has many great articles about using these servers with vmware.

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