How many hard drives on one PSU connector?

Evil-I · 31 Jul 2013 at 16:35

How many 7200 rpm hard drives can I drive from one power output of my PSU?

I have a server with 12 1tb drives in it, where the power cabling is a right old bodge of extensions and splitters, so I was going to make custom cables. Then it occurred to me, how many would be the maximum I should string in one loop?

All advice appreciated!

E-I

darael · 31 Jul 2013 at 17:31

I'd imagine 4, maybe 5 at the most. I wouldn't be comfortable with more than 5, but then again maybe the cables can take more than 5 drives.

The biggest issue will be when the harddrives first power up as that's when they need the most power.

Tealc · 31 Jul 2013 at 17:51

Depends which connectors we are talking about.

Molex peripheral connectors are good for 13A per circuit.

SATA power connectors are good for 4.5A per circuit

A typical hard drive will be rated at say 0.5A on 12v and 0.7A on 5v.

Evil-I · 31 Jul 2013 at 20:54

Thanks both,
so in theory on a 13a molex circuit you could just about do 10 drives

They are installed in groups of 4 so I'll probably do 4x3 and chose carefully whatbcircuits they are powered from.
They are on a 3ware raid card with staggered spin up so I'm not so worried about initial draw.

Appreciate the advice!

E-i

darael · 31 Jul 2013 at 21:07

I've just looked at the specs for a 2TB WD Black and after converting it works out at about 0.9a when reading and writing. 13a shoulld provide for 14 0.9a drives.

darael · 31 Jul 2013 at 21:51

Just occurred to me that I gave the max drives for molex connector, but not SATA. Just divide 4.5a by 0.9a, giving you exactly 5 - so 4 would be safer.

Evil-I · 31 Jul 2013 at 22:20

Thanks mate.

Drives are mixture of samsung f1s and f3 so i'll check the specs on them.

One daisy chain of satas would be neater so might go that route if power usage okay.

darael · 31 Jul 2013 at 23:04

Read/write power consumptions below for SATA connections (4.5a), from spec sheets.
F3 160-500GB: 5.8W / 0.483a. 9 drives
F3 750/1TB: 7.2W / 0.6a. 7 drives.
F1 160-320GB: 6.1W / 0.508a. 8 drives.
F1 500-650GB: 7.4W / 0.616a. 7 Ddives.
F1 750-1000GB: 8.4W / 0.7a. 6 drives.

Evil-I · 1 Aug 2013 at 10:00

Wow, thank you mate.

Had a quick mooch on my phone last night but had real trouble finding the power draw specifications. Was going to look this morning but you've saved me the trouble!

So if I worked on worst case scenario for drives (that they were all 1Tb F1's) 12 drives would draw 8.4 amps, which is easily covered by a 13a molex circuit or would need to be split across 2 x sata circuits.

Getting the side cutters out tonight I think!

Thanks again,

E-I

Evil-I · 2 Aug 2013 at 09:26

Well, daisy chained all 12 hard drives last night by plugging sata connectors in the the drives and running cable straight into them. Talk about a neat and tidy job, well pleased.

Only issue now is I suddenly want to do a proper cable sort on the rest of the box which is a bit pointless as its a server.

Meant to take and post a pic, but forgot.

Anyway, thanks for the help guys, job done!

E-I