Thursday, April 27, 2017

Right-sizing a home-server PSU

I am running a small, Windows 7 based home-server in my home. Its primary function is to serve music to my Squeezebox music player(s), but it also serves as my file server and movie transcoder.

I needed to replace the PSU, but what is a proper size?


In 2012 I build my first proper homeserver (using an I3 board in an old Compaq case), which took a lot of work as that was a desktop case never intended to be used as a homeserver...

This machine (with three HDD's) served me well until 2015, when I decided to replace the I3 in the homeserver with something weaker, as the I3 was simply overkill for me. The I3 is a fantastic CPU and probably the perfect choice if you transcode three of four streams simultaneously, but who does?

Why not go for a NAS? Well, I also run TVersity, AirVideo HD, and BubleUPNP server on that machine, which won't work on a NAS.

(And to be totally honest, that I3 was repurposed to drive the PC my kids use for Internet and some gaming.)

2015 Pentium G3220

More information on the 2015 build you can find here:

  • CPU - Intel Pentium G3220 (boxed)
  • CPU fan - stock
  • mainboard - Asrock H81M-DGS R2.0 socket 1150
  • video - integrated Intel stuff
  • memory - 4 GB Kingston ValueRam
  • system fan - Arctic F12 TC temperature controlled
  • PSU - reusing an old Xion 500W (going to be replaced with a Seasonic OEM 400W soon)
  • case - Antec VSK4000
  • harddrives - bunch of disks I still had laying around

Note that one line... re-using an old Xion 500W power supply... which must have been from 2004 or 2005, just after arrival of the SATA standard. It first served in my primary PC until I bought a Dell XPS710 in 2007 (which still is in use until today, by the way).

I may have used the Xion PSU in some machine when I bought it, but since then it pretty much mostly sat on the shelf from 2007 to 2012. It's dark chrome body still looked like brand new when I used it again.

I did actually use this 'old' power supply in for two more years. Which may or may not have been smart. (If a (bad) supply goes, it can take lots of other components with it.)

What if...

What if your PSU fails? That would depend on the design and quality of the unit. A cheap unit may blow up your complete PC, so perhaps it does make sense to invest in something of sufficient quality.

The second potential problem with a cheaper PSU is that its output may not be 'clean' and 'stable' enough, thus possibly resulting in an unstable home-server, with perhaps data loss.

And finally, cheaper PSU's may use cheaper components more subject to aging. So your PSU may be working fine at the beginning, but how well will it work after a few years? With ageing the quality and capacity of the PSU will go down.

Drive & PSU problems

The actual trigger to replace the PSU wasn't a power problem. I run Harddisk Sentinel on my home-server, and it reported issues with one of the harddrives, a 3 TB Seagate ST3000DM001 (which has a bad reputation if you search for it on the Internet). After replacing the harddrive I noticed that the fan of the power supply, even when in standby mode, was making noise (!)... And I realized perhaps it would be better to replace it. Which had been my intention anyway, two years earlier...

The right size

Lot's of stories on the Internet about proper size for a PSU so go and read them all 😏

My approach:

Bronze vs. Gold

If you buy a new PSU, consider the price difference between a 'bronze' and 'gold' unit. How long will it take before you earn that extra money back?

Let's say it's 2% more efficient, and your PSU runs every year 8 hours per day at 50 watts. You would save 365 days * 8 hours * 50 watts * 2% = 2.9 kWhr. Assuming 1 kWhr = 15 cents, then you'd save 45 cents.

Idle usage

Bronze, silver, gold, platinum etc. only perform well at HIGHER wattage, in other words it's best if your PSU isn't oversized.

Using a 500 W PSU, it would work optimal with usage above 20% x 500 W = 100 W.

There's no telling how good PSU's are BELOW the minimal usage as defined in 'bronze' or 'gold' standards, it all depends on the manufacturer and the model. As a rule of thumb: get a better brand, do not oversize too much, and read the reviews on the Internet.

I measured the idle consumption using a Kill-a-watt clone, and with the old PSU in it reported around 100 W when idle. At first glance that sounds right, but a single Pentium with 4 drives spinning idle should not consume that much power. I knew something was off...

Once I actually bought a 350W Seasonic G 360 PSU the issue became clear: with the new PSU the system would only use 35..40 W when idling. In other words, the Xion PSU wasted 60 W doing nothing. Ouch!

Maximal load and ageing

A PC is using more power during startup and shutdown, when all drives are spinning up and the computer isn't trying to be as power efficient as possible.

I measured the maximal usage during power up (with the Xion PSU still in use) as 160 Watts. Keeping all 4 drives and the CPU as busy as possible it wouldn't go above 165 Watts.

Assuming a supply ages 20% over its lifetime, the minimal size should be around 200 W.

The new PSU

Calculations and measurements indicated a 200 W supply should be enough, but a. there are very few quality supplies that small, and b. it's okay to have a little extra power to handle external USB drives and such.

I looked around and checked out the reviews, then settled for a Seasonic G 360 PSU.


With the old PSU: Xion 500 W, 100 W idle, 165 W peak
With the new PSU: Seasonic G 360, 35..40 W idle, 110 W peak

As the PC is mostly (always?) idling, I'll be saving 60 W whenever it is running. I suspect it may still be wasting a few watts, but not too much. (I could move to a more efficient mainboard with, for example, an Intel Atom, but I want the system to be able to do some transcoding without getting on its knees...)

I expect the Seasonic to use 365 * 8 * 60 / 1000 = 175 kWhr per year, that's 175 x 0.15 = 26 euro / year. So, if I would only replace it to save power I would recover the cost after 2.5 years.

The new PSU is good / big enough to power a slightly better I3 with 6 drives, so I know if this board fails I can keep using this PSU, though I should probably not use it for gaming purposes, at least not with a fancy graphics card 😉

My biggest power consumer is still a Dell XPS720 with a 1 kW PSU. But as a rule of thumb I only replace equipment when it is either broken or unreliable, or no longer fulfills its purpose...

Antec VSK400

One more note on the case. My current home-server is using the Antec VSK400 case, which is a horrible cheap affair, and uses the old configuration where the PSU draws its air from inside the case. The G 360 is wasting little energy, so its fan is not doing much.

The main board I used only supports four drives, so the crazy amount of drive slots were of no use to me. Besides ventilation for the upper drive slots is bad.

To make sure the drives stay cool, I added one temperature controlled fan to the back panel, and taped off the side perforation, making sure incoming air flows over the drives, resulting in the following setup (with taped side vents and added sound dampening material):

I think there is still some room for improvement. At this moment the room is 20 degrees, and all drives idle around 30 degrees. I should have checked last summer, but I forgot...

Update. Indeed, drive temperatures are a bit higher during summer. Room temperature 25, drive temperature 37, quite a bit higher than I expected. I also verified if my cooling approach worked, and at least that's according to plan: when I take off the side panels the drive temperatures go up to 40 under the same circumstances and load.

Update. It seems the latest Windows 10 update (June 2018) fixed sleep / standby issues, and keeps the SIL SATA card alive, even after a warm boot! It's Windows, so one never can tell, but still...

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