Cost saving with intel atom

I've bought intel atom mobo 2 days ago, cause my home server have been consuming too much power.
My plan was to save some bucks and not to struggle too much in performance.
I've bought second hand intel D510MO (cause new atom mobos are too expensive) for 58$ with shipping.
I was a bit sceptical about atom performance, because of my experience with Asus EeePC 901.

My previous home server was 8GB, 2*250GB (raid1) hdd, intel Q9400 with asus mobo. It has been running
5 virtual machines with xen and CentOS. About 3 GB ram was still unused. Cpu was stressed only during backups
and intensive use of rcracki (lm hash cracking), but average load during 24h was like 0.01.
But even in idle this "server" consumes 73W of power and when stressed it goes between 100 and 110W.

I have to cut memory use of some VMs cause atom D510 have 4GB max memory. But after that xen runs smooth.
Firts thing I have to check was power consumption. TDP of Q9400 is 95W, atom D510 is 13W so there should be
a difference. And there is. Idle (serving those 5 VMs without high load) new "server" uses 38W of power. Stressed
(with rcracki) it never crosses 41W. Considering that this machine is stressed rarely I assumend that power save is
35W (73-38). In my city 1kWh of power costs 0.173$, so running this PC 24/7 for a month gives 35*24*30.5/1000*0.173$ average savings,
which is about 4.43$. So I have to wait 13 months to get my 58$ investment returned, and then I start to save money.
I guess I have to wait shorter because prices of energy are constantly growing, but anyway considering that I'm gonna use that mobo
like 3 years there will be some savings.

But what about performance? Before I switched mobos in server, I've checked new atom D510 with ubuntu 10.04. And I was nicely surprissed.
Internet browsing runs smooth, even with high content loaded pages. Youtube runs smooth. Of course overall performance was lower than my
C2D PC, but It was much much better than 32bit Athlon 2400+ that I've been using with this ubuntu like 2 months ago. Work with atom (D510)
with 2GB of ram was nice. And I consider (and recommend) buying something like that for internet browsing.

But what about performance and impression as a server.
First of all there are 2 drawbacks. Atom doesn't have VT-x, so I have to stay with xen and it's paravirtualized VMs. KVM and vmWare is not
an option here. And 4GB max memory limit is kinda low considering ram is cheap and I already have 14GB DDR2 ram.
Subjectively when I've check performance of services served by new machine (for exmaple this site) I've seen little slowdown.
But then I've checked load on VMs, and it looks normal (same as before). I/O performance stays the same (exactly). Network copying large files
from LUKS crypted volume gives exactly the same speed as with Q9400. So its not bad. So I have to check rcracki (high intensive CPU and I/O load).
Old server used 2GB and 2 real cores VM to run rcracki. New one got 2HT cores and 512MB VM. I've tested 7 hashes pack to compare performance.
And results are:
Q9400 got 223s of I/O time, 50s of cryptanalysis and 120s of pre-calculation time.
D510 got 231s of I/O time 193s of cryptanalysis and 614s of pre-calculation time.

So I/O is almost the same, crypto is 4 times slower and pre-calc is 5 time slower. Not bad considering that D5100 have 6 times less L2 cache, 1GHz lower clock
and 2 times slower FSB. VM had 2HT cores instead of real ones and runs with 4 times lesser memory amount. So performance is a good surprise.

Another pro is that new mobo is noiseless, no fans, nothing mechanical to break down, no humming at night.

So I condiser switching to atom is a good idea for small server, internet desktop or even NAS. But when performance is really important matter you should stay with proper dedicated solutions.

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Article | by Dr. Radut