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I'm seeing a blank screen with cursor(underscore) at the top left. My laptop is accessing the hard disk continously. It's been around 15 minutes.

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What command did you use? Just for the record, if you used dd without specifying a block size, it will take an eternity. If you specify a decent block size, it goes quicker.

That said, it depends on so many factors that it's impossible to give you a decent answer. (For example: Disk speed, interface type, whether there are errors on the disk, ...)

My first question is: why do you want to zero it out? If it's for your own use, just repartition. If you want to trash the disk, the most efficient way is to use a nice big hammer on the disk until its heavily damaged. That should stop most amateurs getting any data from it.

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  • It had bad sectors in it. I was getting warning that disk may fail soon. So, I thought clearing it and installing OS will be good. – sushil Aug 16 '16 at 12:43
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    Nope. Trying to repair a disk that way is playing with fire, if it works at all. The disk is good for the trashbin. That's it. Do yourself a favour and get rid of it. – jawtheshark Aug 16 '16 at 12:44
  • @user3664868 the warning that the disk may fail soon refers to the hardware itself. Writing to it even more will just make it worse. – TheWanderer Aug 16 '16 at 12:54
  • Okay. I see your point. I will buy a new one. Thank you for your answers. – sushil Aug 16 '16 at 12:59
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The last time I did this before selling a disc a couple of years ago, dd-ing with a 4086 byte buffer and appropriate numbers for the size of the disk, I was getting 2-3 GB/minute (there's a dd option for getting occasional progress reports, though I forget the details). So a 500GB disc would take around 200 minutes or 3 and a bit hours.

Remember, you've got to generate 500GB of data (that it's all "0" doesn't matter), then write it to the disc. If you're on a USB-2 connector, for example, you'll be limited to 480MB/sec, and 500GB @ 0.48GB/sec is a thousand seconds (18 minutes) even with nothing else happening at all.

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  • It took almost 3-4 hrs and finally ended with an error that says like it was able to do 279gb to zero with speed of 25.9mb/s and input/output read,write error. I don't remember exactly but it was something like that. – sushil Aug 16 '16 at 17:55
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    You are mixing up bits and bytes. USB2 is 480Mbit/sec... 1Byte=8bits, so theoretical transfer rate of USB is 60MByte/sec. That's totally ignoring overhead. 60MByte/s means 0.06GByte/s, which means for 500GBbyte, you need 8333 seconds, also known as 2 hours and 20 minutes. Calculate in overhead and it starts getting closer to the actual results that user3664868 had. (It also matches your stated experience) – jawtheshark Aug 16 '16 at 22:55
  • Oh, and another detail. You most likely meant a buffer of 4096 bytes, which is (for this task) frankly... not enough. That's basically one sector, which won't help you that much. Just give it a bigger buffer. You've got enough memory, right. I usually use bs=1G and let it work. Too small buffer sizes with dd aren't helping as much as you'd think. – jawtheshark Aug 16 '16 at 22:56
  • Ooops, yes. Bits & bytes. Never bothered to experiment with buffer sizes much. Once I'd got something that was working OK (IIRC I did the trick of sending the dd process a signal from another terminal to force a status report), I could leave it working in a corner of the office and get on with paying work. – Rockdoctor Aug 19 '16 at 10:05

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