I’m still learning about
dd. It took me a while to discover it, but now I use it on a daily basis (well, maybe not quite ) to clone systems, backup entire drives, get visual snapshots of the data on a disk or to scramble the contents of a floppy or USB drive.
A couple of days ago I got a 60Gb hand-me-down hard drive that I didn’t want to look at, and arbitrarily plugged it into an always-on machine and put it to work with
time dd if=/dev/urandom of=/dev/sda.
And as promised, it dutifully started dumping random information into the drive, churning away for 10 minutes, 20 minutes, an hour. …
By this point I was starting to itch to use the drive. But it was time to take care of some real-life issues, I let it run while I left the house.
When I came home at the end of the day I expected to see a report, but it was still running. I didn’t have time to fiddle with it, so again, I left it run, this time overnight.
In the morning, it was still going. And at the end of the day yesterday, it was still going. …
And this morning I decided to arbitrarily cut things short. I suspect that over USB1.1 I probably should have employed different flags or block sizes, to avoid a two-day session writing out random nonsense to a hard drive.
But I definitely blame myself for this little inconvenience — after all, I should have thought about what was happening: the transfer of 60Gb of information over USB1.1.
I’m no stranger to slow speeds over USB1.1, and so the little alarm bells should have gone off after only a few minutes. Even USB2.0 would take a while, for something of that size.
In any case, I have learned my lesson. If you want to blank a drive with dd, for goodness sake don’t do it over a slow USB connection.