Hey guys, as I started connecting my 120 HDD farm, I was wondering will it be OK to power all of them with one PSU, probably 1200W or so? In my basic calculations, since the power usage of the drives is less than 10W, if I have sufficient connectors, I can easily power them all. The dilemma is that I am not sure whether the PSU can provide that amount of power through MOLEX/SATA cables or it was designed mostly to power CPU/GPU through their appropriate cables. Does anyone have a similar problem/experience? Can someone recommend the best practice to safely connect 120 HDDs now, with an additional 100 in the next months?
Just to make it more clear, I have a sort of self-made rack and already mounted the 120 HDDs on it and I am prepared to have them connected on more than one PC, I was just wondering can I have the HDDs all connected to one 1200W PSU, either via MOLEX to 5 x SATA adapters or something similar. My math is that I have 5 connectors for the MOLEX/SATA cables on the PSU, so if I connect 5 cables, each of them having 6 MOLEX connectors, and than connect each molex to 5 x sata adapter, the result is 5 x 6 x 5=150 sata power connectors on single PSU. If I can use just 100-120 of those 150 connectors, I will be very happy.
Don’t forget that HDD spin-up takes about a double of the nominal power. I have a JBOD intended for 24 HDDs and it has a 900W server grade PSU. With 18 disks populated, it draws ~ 150W from the UPS when all disks are spinning “idle”.
Over-provisioned? Maybe. But that’s how manufacturer intended it. When you run electrical equipment 24/7, it is recommended not to exceed 80% of the nominal load to avoid fire hazard.
Fuses are made to break at around specified load, and we can assume that it is not exactly as specified. Also, your load may vary a bit with input voltage, temperature, …
On the other hand, if a PSU is a reputable, it is meant to run at 100% 24/7 as it is not meant to sharply break at 100% load. Even if you check efficiency, you will see that they measure it for over 90%. Although, the problem is not really the advertised max power, but rather power delivered per given voltage lines.
Also, as already mentioned, the initial power-up is where the biggest load is. It depends, whether your controller can stagger powering those drives.
Saying that, giving your PSU some headroom is a good idea, but not really worth sweating over it.
I would also like to point to another potential issue. Are those 12V coming through SATA/MOLEX cables on the same “rail” with the 12V for CPU/GPU power? Meaning should I expect to have let say 1000W on those SATA/MOLEX (if the power on 12V is specified on the PSU as 1000W) or that amount of W is usually planned for GPU/CPU power?
I would like to control the initial power-up/spinning power draw, and I think I can do something regarding this by configuring some options on my LSI RAID controllers on which most of my drives are connected. It is that I am still working on decision making regarding PSU model & power, will try to learn about “disk staggering” latter, when I connect everything and start configuring mobo/raid card/software.
No, that is what an electrician or Google will tell you.
“What is the maximum allowable continuous amp load on a 20 amp circuit?”
“Because the load is continuous, multiply 600 volt-amperes by 125 percent (600 x 125 percent = 750 volt-amperes). A 20-ampere, 120-volt branch circuit will carry 2,400 volt-amperes (20 x 120 = 2,400). The maximum number permitted on a 20-ampere branch circuit is three (2,400 ÷ 750 = 3.2 = 3).”
If you ignore this rule your risk of fire goes up dramatically.
I didn’t question your assertion about those fuses. We agree on that.
What I wanted to say is that the logic that applies to those fuses is not what applies to those PSUs, as those two are different animals. PSUs are meant to handle 100% load at 24/7 without any hazards. However, what that 100% is, is not the sum of Watts on all rails (thus the sum of Watts on all connected equipment).
“Good brands have headroom for “100%” load and can do it just fine. The problem is PSU designs efficiency maxes around 70-80% load. Technically if you want to punish your psu you can. If you thing burning your house down is worth the risk, go ahead.Jan. 21, 2018”
You will melt the connectors like that! (or the cables)
Here’s the thing. hdd’s use the 5V rail as well as the 12V rail
1200W PSU has most of it’s power on the 12V rail, maximum 30A on the 5V (typically 25A)
HDD can use about 0,9A on 5V and 1,5A on 12V (check the specs)
So you will overload the PSU for sure with 120 hdd’s
Also 4-pin Molex connector and PSU connector can handle max 156W
Sata connector can only handle 56W total power
(this is 12V + 5V combined)
Long story short you need a way to turn 12V into 5V, see link below for an example.
And then still 120 hdd is too much because the power draw will be 1200W with everything running at minimal, during spin-up of the drives the PSU will shut-down.