custom hw vs cots - power

[Alvin Oga]

hi ya michael

On Tue, 23 Aug 2005, Michael T. Halligan wrote:

> On the note of  Storage, Capricorn's offering looks pretty good. 80TB in one
> rack, according to their #s means 30 AMPS.. at least at my datacenter, 

...

> If those numbers are accurate, then before 
> bandwidth/networking/manpower, you're looking
> at $4k/month including power and space.

lets see ... i didn't calculate power costs/estimates but let's see
for the fun of it ..
 
 20A == at 12V DC per 4U ( 2A per blade * 10 blades ) 
	but it'd needs 5A surge for about 1 second to spin up the disks
	which we'll ignore for simplicity here

	but, additionally, the power supply must be able to provide
	that extra surge current during power on of the blade

	- the above numbers are measured numbers with ammeters and scope

200A == typical power requirement to run 160TB of storage ( 10x 4Us )

2400W == estimated power per 150TB rack ( 200A * 12V DC )

	nice numbers in my book, which is why we're building custom
	systems instead of COTS that cannot meet the customers specs

	- the trick is to get a reliable 500A at 12V DC power supply
	which is available off the shelf
	and of course, get 2 of um to do load sharing at these current
	levels is not a trivial problem

c ya
alvin