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jdizzle
Asked: 2010-05-19 20:56:55 +0800 CST

zeroing a disk with dd vs Disk Utility

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I'm attempting to zero a disk on my Mac OS X machine. I'm going for complete zeros and unformatted, so I think of dd. Unfortunately the maximum throughput I've managed to get out of dd is 7MB/s. Just for grins I tried disk utility and it has a throughput of 19MB/s. What gives? I've tried changing the bs option on dd to all sorts of values, but it still hovers around 7MB/s. Why is disk utility so much faster?

mac-osx dd zero-fill

2 Answers

  1. That sounds pretty slow for dd, what was the infile you were using? I prefer dd to Disk Utility.app just because it's faster and I find it's easier to work with. The command you should use is:

    dd if=/dev/zero of=/dev/[blockdevice] bs=1M

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  2. Disk utility may be faster because it writes to a raw disk. When using DD, try writing dd as a raw disk by putting an r infront if disk in /dev/disk. Therefore your dd command should look like the following:

    dd if=/dev/zero of=/dev/rdiskX bs=16m

    You may want to change the lowercase m after 16 to an uppercase M depending on if you are using dd with mac os or linux.

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