[mdlug] 40tb nas

[Dan Pritts]

On Sat, Oct 17, 2009 at 12:43:22PM -0700, Michael Mikowski wrote:
> Amortize the hardware costs over 3 years, and we are looking at
> about $0.07/month storage cost with unlimited retrieval.

When doing such calculations, don't forget the power and cooling
costs.  They are significant.

With WD 1.5TB "greenpower" drives, 45 drives * 3.7w idle = 166.5
watts for drives at idle.

to make the numbers round, guesstimate 134w for motherboard, cpu,
sata cards, port multipliers; it could easily be more.

Assume 80% efficiency power supply and you are pulling 375w at the
wall; 9 kwh/day.  

I think 80% efficiency might be overstating it.  The PSU they chose
is 80plus certified, but they said they had to overspec it to get
enough 5v power (vs 12v power).  When running at less than full
load the efficiency will be less.

At umich's MACC data center we pay about $.25/kwh inclusive of
power, cooling, and maintenance costs.  

Admittedly, you could get cheaper power and cooling at the cost of
data center reliability.  Let's cut it to $.20 since you're clearly
thinking of doing things on the cheap.  $1971 over your 3 years.

Add that to the $7,867 capital cost, and you have $10,330.

Of course, you don't really get 67 usable terabytes; that is
calculated in "drive terabytes" and does not account for RAID or
filesystem overhead.  I'm guessing amazon sells "drive terabytes"
too, so let's ignore that.

They mention 15-disk RAID6 sets, which ends up as 58.5 TB.

Now that I do the math, I come up with .46c/mo inclusive of power
and cooling, not the 7c/mo you mention.  46 hundredths of a
cent vs 7 cents.

Hee.  One of us can't do math.  Your number passes the sniff test
but I can't find the error in my calculation.

Here's what i get when i try to replicate yours:

$7867 / 36 = $218/mo in capital
58,500 gigabytes 

$218/58,500 = $.0037

If you used the 40,000 gigabytes mentioned in the subject line,

$218/40,000 = $.0055

As far as this being hot and noisy, obviously it will.  So will anything
else that provides this much storage.

danno