After I get my new iMac up and running, I'll be giving the Mac Pro to someone with a pristine system on it. I plan to zero out data on all four internal drives before doing so (I'm not paranoid enough to go for a 7-way or 35-way erase). I intend to boot from the Snow Leopard DVD and use Disk Utility for this purpose.

My question: Since this will take a long time, is it possible to erase all four disks simultaneously or do I have to do them separately? Also, I could use my existing boot drive's copy of DU to erase the other three and then use the DVD to erase the fourth. Would this be any faster than using the DVD for all?

If you're not concerned with maximum security, why not just reformat each drive? One drive at a time shouldn't take more than 10 minutes.

You have a point, but I'm sufficiently paranoid to go further.

If you are truly paranoid you should use an electric grinder on all the platters in each of the drives. Even the 35X overwrite can be read if someone wants to badly enough. Someone like NSA or FBI can do it but even they have to really want the data because it is so expensive and time consuming to recover information that is buried that deeply.

Yup, until it goes through the wood-chipper, it's still available, for a price. All you can hope to do is to make it more expensive than you're worth. I think if the FBI was going through your garbage can, the wood chipper would only be a good starting point.

When you really want to know what it takes to destroy something beyond state-actor-grade recovery, look to the military for ideas.

On a nuclear sub they still have paperwork to dispose of. They run it through a three tier shredder, which shreds it, then cross-cuts it. They're not even close to done yet. Then it PULVERIZES it. i.e. turns it basically into powder. THEN they mix the dust with seawater to form a slurry, and pump THAT out of the sub.

Oh, and a truly interesting thing to muse about if you're bored.... what will future criminals, police, etc, 100 yrs from now think about our garbage dumps? Imagine recycling/reclamation tech that's going to exist at that point, they'll be considering former dumps and landfill sites to be the new oil fields in terms of recoverable materials. (imagine even all the gold you could recover from an entire landfill, if you had the tech? gold? meh. imagine the COPPER!) Now think what they would do if they run into a hdd that you've 3-passed. That may take them five minutes to read. Who knows what the future holds. A lot of people are going to seriously regret and sweat about things they threw away decades ago. We'll see a bit of a row over the ethics of going through old dumps, mark my words.

In answer to my original question, apparently it is possible to erase multiple disks. Look at Preparing Your Hard Drives for Use

I just tried that trick, and it works in Snowy, but I wonder how much faster, if at all, the simultaneous multiple processes will run than consecutive individual ones?

Since you'll no longer need the Pro, this is an ideal opportunity for you to enlarge the body of knowledge... If you zero one drive individually, and then zero the other three simultaneously, it seems like you ought to get a pretty good idea of the relative speeds of the processes. (I don't think the amount of data written to a disk will make a difference.)

This sounds like a good experiment, Artie. I'll post back with the results. Afterwards, I'll do a fresh install of Snowy for the next owner, a lovely 29-year-old redhead who works at our public library. Naturally, I will be happy to provide "technical support". (Don't tell the missus!)

Here is Topher Kessler's advice.

Another option for you would be to buy a USB3 hard drive docking station and keep those drives - no worries about zeroing them!

Thanks, Freelance. I might just do that.

Considering how cheap and useful they are, I don't think any self-respecting geek could go without a usb to sata/ide adapter in his kit. (beware, some of the cheap ones are SLOW)

Second that!

I didn't have a spare enclosure, and I didn't feel like like disassembling, assembling, disassembling, and reassembling the one I had in use, so I bought an adapter to get data off of a dead HDD from my daughter's MB, and it was a life-saver...not even terribly slow, and it was cheap.

(The only reason I knew that such a thing existed was because of one of your posts a few years back. )

Topher has written a more extensive treatment of this thread's topics. Look at How to handle multiple disks simultaneously with Disk Utility