Wiring Advice

[5teve]

Hi Guys

Just looking for some thoughts.. This kind of sits between hard drives / raid cards and workstations to I put it in here..

I am in the process of wiring my workstation up I have 12x spinners 4x SSD. To keep things tidy I have got a heap of sata and molex connectors to modify the PSU power lines.

My intention was to use 1 line to power 8 drives, however the startup current is giving me some concerns. The cable is 18awg - no more than 2 ft long, apparently the cable is good for 16amps max in free air. Hitachi rate the 7k3000 ultrastars at 2a @12v max on spin up, so I would be pulling 16a for around 4 seconds.. then the worst case scenario is 90.4w of load if they are all reading / writing at the same time - split between 5 and 12v on the line. which should be doable

The other line will power 4x spinners and 4x ssd and an optical. This leaves a molex line to power fan controller and any other ancilliaries I may put in..

The drives are going to be connected to a p420 or p822 and i cannot find anything about staggered startup.. which would save my issue.. if anyone knows if this is supported, that would be helpful.

Otherwise, what are your thoughts about loading for the 4 odd seconds at about the cables maximum?

Steve

 

[Chuckleb]

I've never been too worried about overall draw on a line since most power supplies are single rail now. Never thought about it really.

In know the supermicro chassis power 24 drives in the front with very few lines, 3-4 at best. So you should be able to pull enough power without risk of fire.

 

[5teve]

Yeah I hadnt thought about it too much... and then I started! My terminology for line is cable from power supply, My psu is only single rail but has 3 sets of drive / accessory cables coming from it, which i'm calling lines. 600w overall and 42a on the 12v rail.

I'm amazed at the lack of info out there regarding this... but still hopefully my end result could help someone else.

I have been looking at backplanes to see what sort of power configuration they have on them, from what i can see SM backplanes have 1 molex per 3 or 4 drives. The 4 pin molex can take 8-11amps, so this would be right. I do wonder in this instance tho, as 3 molex on an 18awg cable is potentially going to get you to 24+amps.. well out of spec. How would you guys normally wire up a backplane (if using 4 pin molex) would you use 2 connectors on a single line, 3, 4 or something different?

Steve

 

[Deci]

supermicros SAS2 24x 2.5" backplane has 5 molex connectors split over 3 physical cables from the PSU to power it.

 

[5teve]

Thanks Deci

2.5's pull around 1amp spin up and maybe 0.5 on random read operations. So 24 amps on spin up - 8amps per cable run (line) and half that continuously .. I think I'm gonna have to wait for the raid cards to see if staggered spin up is supported... bah.. if only I had patience!

Steve

 

[xnoodle]

I've powered my Norco's (5 molex on the backplane) from two "lines" on a single rail PSU with multiple splitters, but I'm pretty sure I had staggered spin up with either Areca ARC-1680 or the good old M1015.

 

[5teve]

thanks xnoodle.. how many drives did it have on the backplane?

Steve

 

[5teve]

Well i've decided to play it safe and put 6x spinners on each cable / line. 1 cable has 6x sata, the other has 7 sata for 6 spinners and 1 for a splitter to go to the pair of sandisk extreme pro ssd's as i'm fairly sure startup current isnt an issue with them.. i'll be staying under the 16a chassis wiring rating of 18awg even though it will only be for a short period of time.

The sata spacing is custom for my build to keep things as tidy as possible and also involved extending the cables about 8".

1 more cable to make from the molex based cable - molex socket to 3x sata to power 2x ssd and the optical drive. I'm just waiting on the SSD's to turn up.

Steve