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I have a Supermicro 4u enclosure with dual 1400 watt power supply running on 220v. There are 24 drive bays. The power supply is rated at 4amps for the 5v output. If I have 24 drives that requires .75 amps on the 5v, the math isn't adding up in terms of the power supplied. Is the SAS expander board converting 12v to 5v to supply the extra 5v requirements above the rates 4amps?

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  • What's your actual question?
    – ewwhite
    Jan 8, 2017 at 21:52
  • You should consult the manual of your system or contact your hardware vendor for such a question.
    – Thomas
    Feb 6, 2017 at 11:03

2 Answers 2

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I'm not an expert on storage controllers, but it seems to me that the rest of the power is coming from the 12v line. 3.5" hard drives require both 5v and 12v, so the drives are probably getting most of their power from the 12v source. There is no need for the SAS expander board to convert 5v to 12v; the hard drives require both 5v and 12v.

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What exactly are you looking for in this question?

A full Supermicro 24-bay enclosure should use ~400-500 Watts (based on my experience with Nimble Storage and similar JBOD enclosures).

Power supplies can be rated for higher output than they'll ever need to produce.

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  • Heres a little background on where I'm coming from. I'm doing a little experiment where I'm daisy chaining multiple Supermicro SAS2 backplanes. 6 in total. There are no motherboards in any of these. I am using 2x 1400watt power supplies running on 220v from one enclosure to power the other five. The enclosure backplanes are being fed with 14 gauge wires, I basically modified each molex connector for each backplane with heavier wires. These enclosures are then plugged into a Dell 6100 ESXi with a HBA adapter. Everything works flawlessly. I'm running about 50 SATA drives.
    – user394064
    Jan 8, 2017 at 22:09
  • I plugged in a few older SAS drives where the 5v rating is over an amp each and noticed some issues with the drives if I plugged in more than 8. I then realized that I'm hitting a wall with power requirements, but not the 12v, but I think on the 5v as each drive requires 1.5amps on the 5v. This is a learning and experimental process for me so if this sounds a little crazy. I've measured the output of 5v and 12v to see where it stands and when the SAS drives are plugged in, the 5v drops quite a bit.
    – user394064
    Jan 8, 2017 at 22:10
  • So my question is if a power supply is rated at 4amps for 5v and I'm plugging in 24 SAS drives just in a standalone enclosure without my crazy setup, where is the 5v coming from? I also have a 16 bay Dell drive enclosure where the 5v is at 30+ amps. Why such a big difference between Supermicro with 24 bays and Dell with 16 bays? Both are SAS.
    – user394064
    Jan 8, 2017 at 22:11
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    No... Just no. This sounds crazy! Is there a restriction on the amount of power available to you?
    – ewwhite
    Jan 8, 2017 at 22:18
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    Trying to jam more drives onto a single power supply isn't going to appreciably reduce the total amount of power drawn. You are going to be better off in every conceivable way just running mains power to individual power supplies in each enclosure.
    – rnxrx
    Jan 9, 2017 at 0:35

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