2.5" high-capacity hard drives & modern MB's - +5v current overall use?

I am considering a RAID 5 video storage array for primarily read-only use. As I understand it, laptop hard drives use +5v current.

Let's assume I am using a modern 65-95w TDP CPU, very low power video card (since it serves video clients and does not need to encode or decode anything), and a non-overclocked MB with a RAID controller and maybe a couple of TV tuner cards.

What might I expect the average 2.5" laptop drive to consume when reading (mostly) and writing? I can stagger spinup to minimize inrush current, of course, but I am assuming a 2.5" HD operating is going to draw around .8 amps max or 4 watts during operation. Does that sound about right? I don't need enterprise or SAS grade drives spinning at 10K or 15K, just plain old 5.4K RPM SATA II drives.

And for the sake of argument, let's say I am using an OCZ Z850 power supply that can supply +25A on the 5v rail. I'm assuming that the +12v rail is not relevant in the case of a laptop drive, but I don't know what the average modern, non-overclocked motherboard would draw off the +5v rail on its own. And I use OCZ simply because they have a decent reputation and 850 watts overall PSU does not get into the larger dimensions that can cause case fitting issues.

Any help would be appreciated, especially in computing the "average" +5v current the motherboard will draw on startup and during operation, so as not to overload the +5v rail overall. Then I can factor in how much the laptop hard drives will draw.

Your laptop drives shoudl work, regardless. Their power draw is minimal... as they will run on a USB 1.1 or 2.0 external enclosure.

Yes, my only concern was if I was getting into larger sized arrays, say 6 or more.

I know many 2.5" USB enclosures actually have 2 USB connectors, one for power and data, and one for power only, so I am assuming at some point the drive is drawing greater than 1/2 amp, and as I understand it, a modern PSU must supply a minimum of 18A at +5v to the motherboard alone, not counting floppy drive, optical drive(s), and 3.5" hard drive(s).

Thanks again for the reply.

Still not a problem, if you know how to set up arrays... and not many of them would be running at the same time anyway... Look at the power draw of a 3.5 inch drive.

USB connections are limited too 500ma each; the voltage is not the issue.

Many external HDs attached via USB run into this issue. The solution is to use an external
power supply to the external enclosure and thus avoid using the USB available power at all.