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RAID 5: How much power?

384 Views 5 Replies 6 Participants Last post by  Keh
I just set up my first media server with a 3Ware 7506-8 card.

I have five 250gb drives plus a separate 30gb drive for Win Server 2003.

I'm using an old box: Athlon 1ghz, 512mb, and a 300W power supply.

Question: Is the 300W power supply sufficient? Or should I buy more power.
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Depends on the details. Look in the manuals for your motherboard, cpu, drives, and all the other parts and add up the power requirements. I suspect 300 watts might be marginal but it simply isn't possible to know with what you've given us.
Most of the "older" systems had weak PSU. I had a SuperMicro MB that refused to boot at power on - had to hit the reset button to make it work. Had large number of hard drives attached to the PSU. When I replaced the PSU with a true 400W unit the reset problem went away. You can't hurt the system by going with a larger PSU but an undersized unit can cause problems. Most hard drives use a large amount of power during startup. When they are up and spinning the power requirements drop by more than half. If you can stagger spin the drives that would help.
I have a raid5 box running linux -> 1ghz Athlon, 512mb (similar specs to yours) but I'm running 8 x 200 gig drives on a 3ware 78xx card, plus a 120gig general purpose drive, and a 30gig boot drive.

I was using a 400w psu, but occasionally I'd lose a drive to power issues. I upgraded to a 560w psu, and all is good.


What you didn't mention is who made the power supply. I have had good luck with high quality supplies running setups that they were way underrated for. I just retired a 235W Sparkle that was running an Athlon XP2400 512MB ram,2x80GB, CDRW and a ATI Radeon 9000. All rails ran within spec. I finally upgraded a little while ago when a client went to a 500W so I got his old 400W Fortron. Didn't make a difference in my system but its nice to have the extra capacity. I've been installing 300W Sparkles in client systems for the last few months and have had no failures out of 7 installs. A couple of these are what I would call "challenging" configs. Not a huge sample but if there was some limitation on the capacity I would have seen it already.

I for one would trust a high quality, low rated PS (like Sparkle/Fortron, Antec, Delta, PC Power&Cooling) over a high watt generic. The fact that you are adding 6 HDDs to your system may tax any low-rated PS so you may want to upgrade. If you do, don't get carried away by the wattage ratings. A high quality 400W will run better than a no-name 500W.
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Also, there is the question of which rail is used to power the CPU. Some AMD-CPU mobos use the +5.0 rail rather than the +12.0.

And older Athlons really draw power.

The main factor is the spin-up load of the drives - I note that the card does provide for a staggered spin-up and I suspect it may be your only hope.

If you get past the P.O.S.T./spin-up, you'll likely run OK. But that does not mean that the PSU is not overloaded.

Most are.
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