mac - Does A Hard Drive's Read / Write Speed Affect The Speed Of A Data Wipe / Erase / Sanitise?

I have multiple hard drives that I need to test & Wipe. I have testing software (Drive DX) for my MacBook and I'm using Apple's built-in Disk Utility to wipe the drive to DOD 5220.22-M standard. I am using a hard drive docking station to connect to my MacBook.

My issue is time. It is taking an excruciatingly long amount of time to test and wipe. The full test is around 2 hours for a 1TB drive, which isn't awful but could be better. The wipe seems to go on for hours and hours without an end in sight. (It's a 7 pass wipe which I know takes some time but it shouldn't be that long!)

My current HDD Docking station is USB 2.0 (data transfer of just 480mb/s). I was about to invest in a docking station that will connect either to the USB 3.0 (5GB/s) or the Thunderbolt 2 (20GB/s) on my MacBook - but stopped myself as I ask this question.

Will the data transfer speed of the Docking Station / Cable even matter if the Hard Drive has a Read / Write speed of say 100Mb/s? Does that affect how quick I can test & Wipe the HDD? And Does data transfer speed affect the speed of which I can test / wipe anyway?

(I'm sorry for the essay, any help will be much appreciated!!)

Answer

Your computer/OS doesn't have a way to issue a "go off and do a 7-pass wipe of yourself" command to your hard drives. So to do a 7-pass wipe of a 1TB drive, your computer has to write 1TB of zeros to the drive, then 1TB of ones, then 1TB of random data, et cetera. So your computer has to write about 7TB to the drive. That's 7,000,000,000,000 bytes * 8 bits per byte = 56,000,000,000,000 bits that your computer needs to write to your drive for a 7-pass wipe of the whole drive. If you've connected your 1TB drive over USB 2.0 High Speed (480Mbps), divide that 56 trillion by USB 2.0's 480,000,000 bits/sec and you get 116,667 seconds = 32 hours = 1 day, 8 hours.

But USB 2.0 is famous for not really having 480Mbps throughput. It's probably more like 200Mbps, which works out to about 78 hours (about 3 days, 6 hours) for your 7-pass wipe of a 1TB HDD over USB 2.

So, yes, for fastest 7-pass wipes, connect your HDD to your computer via a bus whose real-world throughput meets or exceeds that HDD's max sustained sequential write speed.

Edited to add: Also, please be very careful about units. HDD manufacturers use standard decimal SI units of 8-bit Bytes. So a 1TB HDD stores 8 trillion bits. The read/write speeds that your HDD maker claims are also in standard decimal SI units of 8-bit Bytes, so an HDD that claims a 100MB sustained/sequential write speed means 100 million bytes per second, or 800 million bits per second.

In contrast, I/O bus speeds (besides SATA) are almost always in standard decimal SI units of 1-bit bits per second. So USB 3.0 "SuperSpeed" is 5 billion bits per second, USB 3.1 gen 2 "SuperSpeed+" is 10 billion bits per second, Thunderbolt 1 is 10 billion bits per second, Thunderbolt 2 is 20 billion bits per second, and Thunderbolt 3 can supposedly get up to 40 billion bits per second.

I don't know what the sustained sequential write performance of your HDD is, but if it's, say, 100MB/sec = 800Mbits/sec, then a 7-pass wipe is going to take at least 19 hours no matter how fast of a bus you use to connect it to your computer.