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PSU load issues with 27+ HDDs

R

Ralph_McCloud

n00b
Joined
Mar 30, 2010
Messages
10
Howdy,

I recently stumbled upon an issue with the PSU in my current fileserver setup (Tagan TG800-U26) when performing a cold boot. It seems to be able to handle up to 27 HDDs just fine (no staggered spinup), but as soon as a 28th is connected before starting up the machine, it will try to spinup the disks, shuts off after a few seconds and then turns on again, running into an endless restart loop.

I assume this to be an issue of inrush current associated with having that amount of disks spinning up at the same time, as I can start fine with 27 disks and then connect the remaining disks once the others have spun up.

The question would be, if this is a problem with the 12V rail (64A), the 5V (28A) or if it could simply be due to a wrong connection setup (too much load on one of the rails causing the OCP to shut the PSU off). Maybe one of you has any experience what kind of PSU specs are needed to essentially cold boot with ~35 disks.

The basic system consists of an Intel C2D E6420, 4 mem modules, Gigabyte P35-DS4 board, sas hba+sas expander, an old Matrox Mystique PCI GPU and around 8 fans.
Note that staggered spinup would not be an option here as the SAS expander does not support it.

I would appreciate any ideas :)

Regards,
~Ralph McCloud
 
You'll need to look up the power draw specs on each of your drives. Your drives may vary from this considerably, but here is one example I chose totally at random:

2TB Western Digital Caviar Black (WD2001FASS)
Startup Current +12V: 1.16 Amps
Startup Current +5V: 0.60 Amps
Read/Write: 10.70 Watts
Idle: 8.20 Watts
Standby: 1.30 Watts
Sleep: 1.30 Watts

I have little doubt that you have found the limit of the 5V rail on your PSU. You will need to look at PSUs that put more amps than usual on the 5V rail. If you made an assumption that you are using an average of 1 amp per HDD on spinup (which appears to be the case here) then you'd need to look at PSUs with more than 36 amps on the 5V rail.

A very quick look at the PSUs that HardOCP has reviewed lately shows a 1300W PSU with 24A on the 5V rail and a 750W PSU with 25A on the 5V rail, so bigger PSUs don't necessarily mean better for your purposes. I suspect that most people who deal with such large raids use multiple PSUs.
 
Hi evilsofa,

thanks for your detailed reply. I initially also suspected the 5V to be the cause, yet it irritated me as when I detached one of my old Samsung HD204UI and replaced it with an HGST 4TB NAS drive (Sammy should be 0,7A on 5V and HGST 0,45A), the system would run into the power issue again, hence I guessed that the 5V, while still an option for possible cause, would probably only be a secondary issue. As the Samsung has 0,5A @ 12V and the HGST 0,85 I assume the primary issue is on the 12V rail.

But you are correct, even with high wattage PSUs, many of them have only 24-28A on the 5V rail, which can mess with this kind of setup :)

As far as I know there currently are only Corsair PSUs with >1200W and 30A available, while I think Thermaltake had some 40A Toughpower PSUs a while ago.

I guess one of those could maybe solve the issue. Then again the Corsair HX1200i e.g. shows 100A on the 12V rail, so I assume it to be single rail, which I heard could in special cases like this, cause potential damage to the components due to no OCP, hence the cabling could be melting under the load. Please correct me on this if not true.

Regards,
~Ralph McCloud
 
First thing I would do is get rid of that Tagan. Tagan is a mixed bag seller that primarily sells PSUs from crap and mediocre OEMs. I wouldn't be surprised if your issue has to do with the quality of your PSU rather than any inherent power limitations. I would get either a higher quality PSU with what GotNoRice linked, or a server PSU, which generally has a lot more power available on the 5v line.
 
I dunno about any PSU on the market currently that has that much go on the 5v rail.

You're either going to have to use two PSUs or get a expander that does support staggered spin up.
 
And you do not need a special PSU, any PSU can be added as extra with some wiring and a relay on the green wire. Or you can buy adapters on ebay for $10-15.
 
Thanks for the replies :)
@Tsumi: The Tagan has been holding up pretty well for over 8 years now, so I can't complain in that regard.

Yeah I thought about using a Y-cable for the ATX connector to attach a 2nd PSU, but that would be overkill imho, as the issue only seems to be the startup load. As far as I know I can't just combine 2 PSUs and have one of them shutdown again once the load drops under a specified value, hence I would rather prefer either a single PSU or any alternative solution.

There are e.g. HDD power switches available (BZ-H06), which may be an option. Then again this would mean all power gets routed through there and I doubt the thin cables it uses could hold 6 hdds per channel.
 
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