Q: Mac Pro hard drives going bad in one bay

If you have a Mac Pro 1,1 2,1 or 3,1 the 5 Volt and 12 Volt supplies are present in the Molex power connectors in the Optical Drive bays. The two center pins are grounds, and the outer pins are 12 Volts and 5 Volts respectively. At those connectors, you should see a Voltage slightly higher than the nominal Voltage, e.g., 5.1 Volts for nominal 5 volts, and maybe 12.2 Volts for nominal 12 Volts. Voltages lower than the nominal Voltages could indicate a very rare power supply problem.

The measurement should be made from an outer (voltage) lead with one probe to either inner (return) lead with the other probe. If you do not have a Voltmeter, they can be obtained for under US$20, and in the long run are good for checking batteries and power outlets around the house as well.

Power connectors[edit]

Standard connector[edit]

Pin #		Mating	Function
—			Coding notch
	1	3rd	3.3 V
	2	3rd
	3	2nd
	4	1st	Ground
	5	2nd
	6	2nd
	7	2nd	5 V
	8	3rd
	9	3rd
	10	2nd	Ground
	11	3rd	Staggered spinup/activity (in supporting drives)
	12	1st	Ground
	13	2nd	12 V
	14	3rd
	15	3rd

 

https://en.wikipedia.org/wiki/File:SATA_power_cable.jpg

 

A 15-pin SATA power connector; this particular connector is missing the 3.3 V (orange) wire.

SATA specifies a different power connector than the decades-old four-pin Molex connector used on Parallel ATA (PATA) devices. It is a wafer-type connector, like the SATA data connector, but much wider (15 pins versus seven) to avoid confusion between the two. Some early SATA drives included the old 4-pin Molex power connector together with the new 15-pin connector, but most SATA drives now have only the latter.

The new SATA power connector contains many more pins for several reasons:^[32]

• 3.3 V is supplied along with the traditional 5 V and 12 V supplies. However, very few drives actually use it, so they may be powered from an old 4-pin Molex connector with an adapter.
• To reduce impedance and increase current capability, each voltage is supplied by three pins in parallel, though one pin in each group is intended for precharging (see below). Each pin should be able to carry 1.5 A.
• Five parallel pins provide a low-impedance ground connection.
• Two ground pins, and one pin for each supplied voltage, support hot-plug precharging. Ground pins 4 and 12 in a hot-swap cable are the longest, so they make contact first when the connectors are mated. Drive power connector pins 3, 7, and 13 are longer than the others, so they make contact next. The drive uses them to charge its internal bypass capacitors through current-limiting resistances. Finally, the remaining power pins make contact, bypassing the resistances and providing a low-impedance source of each voltage. This two-step mating process avoids glitches to other loads and possible arcing or erosion of the SATA power connector contacts.

from wikipedia article on SATA

If you are going after this. I recommend the Optical Drive bay cables.

Are those the same drives that were giving you trouble before?

You may just be having unusually bad luck with drives.

The wiring harness for the dives mates with the motherboard at one end. You could try re-seating it, and if that does not work, it is not too expensive to just replace it with a used one.

Anyone else reporting these symptoms was just having very bad luck with drives.

There is no one who has reported such a sage here, so there is on known advice to give you.

I've had a couple of WD Black drives in my 2010 Mac Pro, including the stock 1TB drive that shipped with the machine, so I don't think that this is the whole answer. Maybe a bad batch from the manufacturer?