How Much Power Will My RAID 1 Unit Draw?

November 2, 2010 10:49 AM

I've ordered a RAID 1 unit. It's not here yet, but I need to get an idea about how much power it draws prior to making a decision on a new UPS. It's a 2TB NewerTech Guardian Maximus RAID 1 unit. (Two Hitachi drives inside). Tech support says it draws a maximum of 36 watts. The online specs rate the power supply at 4.2 amps, which, multiplying volts by amps, works out to well over 400 watts. That is, if thats a valid measure of power consumption. Anyone have experience with this or a similar unit and how much power it draws?
posted by justcorbly to Computers & Internet (8 answers total)

It looks like you're calculations are wrong, you're off by a factor. For it to pull 400watts, it would need a 400watt+ power supply. I really doubt it has that large of a power supply. From experience, 36 watts sounds right.
posted by geoff. at 11:16 AM on November 2, 2010

That's probably the output rating for the DC output which will be more like 12V or something. 9V would give the 36W figure. The input current draw is probably a lot lower, more like .5A which assumes a certain level of loss in the PSU. The web spec sheet is indeed rather terse to the point of being misleading.

The Hitachi drive spec sheets indicate the drives themselves draw less than 10W and the control board is unlikely to draw much more than 20W so I think 36W sounds like a reasonable figure.
posted by GuyZero at 11:17 AM on November 2, 2010

Here's the actual power supply. It's rated for 4.2A at 5V and 3.0A at 12V. ((4.2 amperes) * (5 volts)) + ((3.0 amperes) * (12 volts)) = 57 watts. Plenty of overhead for a couple drives and a control board.
posted by zsazsa at 11:21 AM on November 2, 2010

Response by poster: Thanks all. Quick responses. I'll round off zsazsa's answer and go with 60 watts.
posted by justcorbly at 11:25 AM on November 2, 2010

That's the power output. The supply is rated at up to 1.3A on the input side meaning it could, in theory, draw up to 150W. Assuming 50% loss is not excessive so I'd expect at a 60W output level it would easily draw 120W. The 1.3A figure is probably for the lowest rated voltage which is 100V so I'd expect that the real upper limit is 130W, which is pretty close to the 50% loss figure for 60W output.

Having said all that, that's the max rating and the device itself probably draws a lot less. Otherwise the power brick would be giving off as much heat as a 60W lightbulb which is probably the regulatory limit before it's considered a fire hazard.
posted by GuyZero at 11:38 AM on November 2, 2010

Hard drives don't require that much power. Hitachi's data sheet lists the idle power of a 7200 RPM 1TB Deskstar 7K1000.C as 4.4 Watts. Even at spin-up, the event which requires the most power, most drives don't require more than 15-20W or so, and that's only for a few seconds. Most of the time it's around 10W or less. 36W sounds like a very reasonable figure for two drives plus interface.
posted by Rhomboid at 12:12 PM on November 2, 2010

Don't forget that UPS ratings aren't straightforward, either. Sealed lead acid batteries are usually given their amp/hour ratings based on a half load. So a 12 amp/hour battery will actually give you 6 amps over 2 hours. Draw all 12 amps and you won't get nearly a full hour.

UPS ratings are similarly over-enthusiastic. Don't forget that a 1000va UPS WILL NOT power 1000 watts. It will probably be more like 720 watts. In my experience, UPS units that are fully loaded up don't last all that long and kill batteries pretty quickly. I would always size a UPS at about double whatever the normal usage will be.
posted by gjc at 3:14 PM on November 2, 2010

Response by poster: >> ...UPS ratings are similarly over-enthusiastic.

I want the UPS to trigger a shutdown of whatever is attached to it, not to keep things running, even for a few minutes.

That only needs to work overnight. If I leave town, everything is turned off.
posted by justcorbly at 3:22 PM on November 2, 2010