Re: Busted disks caused healthy ones to fail

[Brad Campbell <brad@wasp.net.au>]

Jim Paris wrote:
>>It's not that hard.
>>I have 4 drives loaded in the rear bays and 2 x 5 Way SATA Hotswap bays in 
>>the 6 front 5.25 inch bays. 14 Drives. And yes, they are on a single 420w 
>>PSU along with the motherboard, Athlon XP 2600+. and 5 80mm fans. Not much 
>>else though.
> 
> 
> !!!!!!  Holy crap!
> 
> Let's pick a random typical hard drive, a Seagate 120GB SATA:
> http://www.mittoni.com.au/catalog/product_info.php/products_id/1690
> It lists maximum current draw as 2.8 A on the +12V line.
> Multiply that by 14 drives and we get __39.2 amps__.

Now, lets actually pick my hard drives shall we?

Max current draw on the 12v line is 1.56A at spinup, dropping to 600mA at seek and 556mA at Idle.

So _worst_ case is 21.84A for about 2 seconds (which does actually exceed the PSU ratings by nearly 
3 amps). This machine only gets power cycled about once every three months and I did actually 
monitor the 12V rail with a CRO to check specs and ripple and they never budged.

Worst case running load is 8.4A which leaves ~10A on my 12V rail for my motherboard. Ample.


> Now let's pick a random 420W power supply:
> http://www.newegg.com/app/viewproductdesc.asp?submit=Go&description=N82E16817103445
> Note how it's +12V output is rated for only __15 amps__.

Now lets pick my power supply http://www.wasp.net.au/~brad/p1000256.jpg

So yes, on spinup I'm exceeding my 12V rail by 3 Amps for about 1.5 Seconds (Which this supply has 
amply proven capable of handling). Outside that I don't see an issue.

> Your numbers might differ a bit.  But it is NO surprise that your
> drives are failing.  The surprising part is that they and your power
> supply have worked this long.

I never said anything about failing disks! In fact, if you check back you will see me commenting I 
have a bucket load of Maxtor Maxline-II drives in there that have been flawless to date. (In fact I 
have just ordered 25 more, 15 for me and 10 for a mate. That should increase the sample a little) 
They all sit at below 40 Degrees C and the PSU remains quite cool. (I'm an electronic technician by 
trade and have several thermocouples I use to verify measurements).

Here is the reason the drives stay nice and cool. http://www.wasp.net.au/~brad/p1000250.jpg

-- 
Brad
                    /"\
Save the Forests   \ /     ASCII RIBBON CAMPAIGN
Burn a Greenie.     X      AGAINST HTML MAIL
                    / \