Question 8x HDD Array circuit planning

[chilltemp]

I'm building this disk array enclosure to attach to my NAS. I've sketched the v0 circuit diagram based on the photos and description form the original designer. But I'm concerned that it can't handle the power requirements of the enterprise HDDs I bought (source, spec). Everything I've found online and in the HDD spec indicates that the 12v rail should be able to handle 2 amps peak. For a total of 16 amps when all 8 drives spin up at the same time. I know just enough to be dangerous So I asked my friends and came up with these diagrams.
* One friend recommended looping the power connections as shown in diagram v4
* Another friend was worried that would create problems via a ground loop. Loops removed in v5

Notes:
* 5v rail only needs 3.5 amps
* If I've read the spec correctly, the Minifit & Microfit Jr connectors used by PCIe & my power supply should handle at least 6 amps per conductor with 18 awg wires. Allowing 18 amps for 3 x 12v and 3 x common. BUT, I just learned that the PCIe connector spec only allows 6.25 or 12.5 amps. So, I may need to adjust my circuit to handle more power from PCIe.
* I haven't accounted for peak vs normal load. I'm not sure how to determine the frequency and duration of peak usage. So I think it's safer to design for peak as if it were near constant.

You advice would be appreciated.

Diagrams

 

[kanewolf]

I'm building this disk array enclosure to attach to my NAS. I've sketched the v0 circuit diagram based on the photos and description form the original designer. But I'm concerned that it can't handle the power requirements of the enterprise HDDs I bought (source, spec). Everything I've found online and in the HDD spec indicates that the 12v rail should be able to handle 2 amps peak. For a total of 16 amps when all 8 drives spin up at the same time. I know just enough to be dangerous So I asked my friends and came up with these diagrams.
* One friend recommended looping the power connections as shown in diagram v4
* Another friend was worried that would create problems via a ground loop. Loops removed in v5

Notes:
* 5v rail only needs 3.5 amps
* If I've read the spec correctly, the Minifit & Microfit Jr connectors used by PCIe & my power supply should handle at least 6 amps per conductor with 18 awg wires. Allowing 18 amps for 3 x 12v and 3 x common. BUT, I just learned that the PCIe connector spec only allows 6.25 or 12.5 amps. So, I may need to adjust my circuit to handle more power from PCIe.
* I haven't accounted for peak vs normal load. I'm not sure how to determine the frequency and duration of peak usage. So I think it's safer to design for peak as if it were near constant.

You advice would be appreciated.

Diagrams

Commercial NAS units do staggered spin up. 2 drives, wait some time, then the next two, etc.

 

[chilltemp]

Commercial NAS units do staggered spin up. 2 drives, wait some time, then the next two, etc.

True. And my HBA supports staggered spin-up. But, after the startup it's up to the OS to manage standby & spin-up. Unfortunately, UNRAID only supports staggered spin-up at boot, not after putting drives in standby.

16 amps (12v 192 watts) is not a lot for a modern power supply. It's just a matter of safely supplying to to the drives. My two main ideas are:
* Supplying it from the main power supply (which is currently underutilized) as I'm designing for above.
* Using a FlexATX PSU in the drive enclosure. But those typically only natively support a couple of drives. So I'm still left making custom connections. Making sure to always turn them on & off in the right order (trivial, but easy to forget). And, do I need to interconnect the grounds of the two PSU's?

EDIT: Third option, staggered start but never use standby.

DIY can be challenging but it's fun.

 

[kanewolf]

True. And my HBA supports staggered spin-up. But, after the startup it's up to the OS to manage standby & spin-up. Unfortunately, UNRAID only supports staggered spin-up at boot, not after putting drives in standby.

16 amps (12v 192 watts) is not a lot for a modern power supply. It's just a matter of safely supplying to to the drives. My two main ideas are:
* Supplying it from the main power supply (which is currently underutilized) as I'm designing for above.
* Using a FlexATX PSU in the drive enclosure. But those typically only natively support a couple of drives. So I'm still left making custom connections. Making sure to always turn them on & off in the right order (trivial, but easy to forget). And, do I need to interconnect the grounds of the two PSU's?

EDIT: Third option, staggered start but never use standby.

DIY can be challenging but it's fun.

Disk drives like constant. Leave them spinning 24x7, IMO. I have worked in data centers with thousands of disks. They never spun down.

 

[BFG-9000]

You know how they say 90% of engine wear is from cold starts? Once spinning, fluid dynamic bearings have no metal-to-metal contact and therefore suffer no wear. In constant use they last until the seals fail and the oil leaks out. So the only minus is increased idle power consumption.

Of course now the carmakers have gone to stop-start technology to improve mileage by 2%, but I don't think they are interested in you keeping your car much past the warranty period.

 

[chilltemp]

"Should I spin-down the drives" is probably the most heavily debated topics in the UNRAID forum. With the size of my current array, it's probably not worth spinning down the drives to save $40 a year. The savings goes up as I expand the array and electric rates continue to rise (say saving $80/yr when I max out the array with the projected electric rate increases).

Realistically, my array is used for archival. It's backups and camera recordings (no live writes). With directory caching, scheduled writes, and the way UNRAID allocates files; only a couple of drives are expected to be used in a day. I could set the standby timer to 24 hours to prevent drives from spinning down / up very often. Half my drives could be in standby for weeks at a time.
With that said, I'm still not 100% convinced on either side of the spin-down argument.

"but I don't think they are interested in you keeping your car much past the warranty period."... Yeah, I'm not even convinced they care that much. It's more like "we can get away with X, so why pay for more".

 

[Misgar]

it's probably not worth spinning down the drives to save $40 a year

Oh for cheap electricity where I live. I've just worked out if I leave one of my 8-disk TrueNAS Core servers running 24/7 for a year, at a nominal 120W it'll consume 1051.2 kWhr and at the equivalent of US $0.32 per unit, that equals $336 per annum. I don't run them continuously.

I've not observed any problems allowing 8 or 10 Enterprise disks to start simultaneously, provided I feed them with high quality PSU. I can't open your Imgur link at the moment so I cannot check your propesed wiring diagrams.

Some of my builds use SAS, others SATA, but I haven't implemented power-on delays for pairs of drives. When I worked in data centres, I used professional systems provided by my employers. At home I'm less fussy, but I do keep multiple backups.

So I think it's safer to design for peak as if it were near constant.

Peak current draw on the 12V rail of a hard disk is when the motor spins up. The platters should be up to speed in a few seconds and then the current reduces. Drive manufacturers mention peak and normal running currents in their specs. Check yours out.

Cables can cope with brief overloads. So can connectors. Go too far and things burn out, but if a high quality PSU cable has three or four SATA power connectors on it, I use them as required.

Don't "over think" the hard disk power connections. Massive overkill is a waste of time and effort.

 

[chilltemp]

The only real challenge is getting the power safely from the internal PSU, to the external enclosure. Putting the total amps from 8 drives down a single cable & set of connectors was the challenge. My latest diagram only includes half the drives. With a much more reasonable total current. I can simply duplicate the circuit to include the other half (excluding the fan & led).

The drives I purchased have a peak of just under 2 amps. They can reach that at spin up, and during certain RW operations. For 4 drives, the combined peak amps would be:
12v - 8 amps
5v - 3.2 amps
common - 11.2 amps

As for overkill... That's my speciality I'm enjoying learning a bunch. Here's v8 of the diagram. I haven't re-calc'ed the correct gauge wires yet.