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Exceeding PS's Rating At Startup: Problematic For Discs?
I just added a new drive cage to a WSH box I am using to back up my NAS
box. Total drives to be 13 (a system drive plus 12 data drives) It only has to run intermittently - when I do my weekly backups of media files. Current PS is rated for 580w and, steady-state the box is pulling high fours, maybe into the low fives. But at startup, there is a surge that goes well into the high six hundreds. Coincidentally, I've been having some intermittent problems with the six new drives that are hanging on a couple of RAID cards. The surge lasts less than 20 seconds. Could that be a problem? Might I be setting myself up for a string of problems in the future? Or is it OK as long as the PS doesn't just stop working? -- Pete Cresswell |
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Exceeding PS's Rating At Startup: Problematic For Discs?
(PeteCresswell) wrote:
I just added a new drive cage to a WSH box I am using to back up my NAS box. Total drives to be 13 (a system drive plus 12 data drives) It only has to run intermittently - when I do my weekly backups of media files. Current PS is rated for 580w and, steady-state the box is pulling high fours, maybe into the low fives. But at startup, there is a surge that goes well into the high six hundreds. Coincidentally, I've been having some intermittent problems with the six new drives that are hanging on a couple of RAID cards. The surge lasts less than 20 seconds. Could that be a problem? Might I be setting myself up for a string of problems in the future? Or is it OK as long as the PS doesn't just stop working? You could look for a means to implement "staggered spinup". We used to be able to do that on SCSI, but I don't know how that translates on SATA. If you have Hot Plug capability in the driver (AHCI), you could always fit a power switch on each hard drive. Leave the ground path intact. Interrupt +5V and +12V with the switch. Switch on one drive at a time, or switch on small groups of drives. During spinup, drives can use as much as 12V @ 3A for the first ten seconds. If you manage to find the documentation for your drive, that info will be available. Many years ago, the current flow level might have been 12V @ 2A, but it's actually heading in the wrong direction. After spinup completes, there are only frictional losses as the heads fly over the platter. My 2TB drive, the 12V drops to 0.51A. My 120GB IDE drive (old news), the 12V right now is 0.45A. (Those are measured values with my clamp-on DC ammeter.) So the steady state value tends to be less of an issue for the average home setup. But if you're spinning up 10 drives at 3 amps each, that's 30 amps load from 12V for the first ten seconds. For the first 0.35 sec, the power supply does not police the current limit. For the other 9.65 seconds, the power supply will monitor 12V flow, and do something if you draw too much. The trip level should be set around 30% higher than the value on the PSU label. The supply will become "soft" near that limit, so the voltage might not be exactly 12V as the overcurrent trips. If the 12V rail drops to 11V, a drive will actually spin down. So if there is enough of a drop, the drive might take action itself. Don't be overly pessimistic in your power calculations. A lot of stuff on the computer, doesn't run at full power during every phase of operation. Even my dual core "65W" CPU, only draws 36W flat out running Prime95 (two threads). And it draws around 13.2W when idle. Depending on your CPU, the consumption can be quite thrifty. You would need a monster, ancient video card, to be hitting 400W at idle. My current processor uses a bit more, at 43W running Prime95, out of a TDP rating of 65W. Early S478 processors, their flat out numbers were very close or a watt or two higher than the listed TDP value. So, yes, I'd be concerned. 13 drives @ 3 amps is 39 amps for the first ten seconds. And you should see if there is some way to stagger that. In a storage server, the rest of the 12V consumption might be less of an issue (you're not likely to be running a pair of 8800GTX in there). The disks don't mind what you're doing, until the yellow wire drops below 11V. I think the 5V rail is monitored as well, but it doesn't have that big surge on it. Only the motor supply (+12V yellow wire) has the big current draw. Paul |
#3
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Exceeding PS's Rating At Startup: Problematic For Discs?
So you can put bread inside the computer to toast it? Your computer is not drawing anywhere near the power hyped by those only told to buy 800 watt supplies. How many watts does a disk drive use when connected to a computer via USB? Well, if the USB outputs more than 2.5 watts, then the computer declares a surge.
Typical disk drives do not draw the massive currents preached so often by a majority who never learn the numbers. Paul has provided numbers that are based in knowledge. Most computers draw somewhere between 200 or around 300 watts maximum in very short bursts. And average much less power demand most of the time. Otherwise your computer could also be your toaster. |
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