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Re: [OT] Lying hard drives [was Re: shutil.copyfile is incomplete (truncated)]

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Date Sat, 13 Apr 2013 13:43:57 +1000
Subject Re: [OT] Lying hard drives [was Re: shutil.copyfile is incomplete (truncated)]
From Chris Angelico <rosuav@gmail.com>
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On Sat, Apr 13, 2013 at 1:17 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Sat, 13 Apr 2013 03:33:29 +0100, Nobody wrote:
>> If you want to wait for the data written to be written to the physical
>> disk (in order to obtain specific behaviour with respect to an unclean
>> shutdown), use f.flush() followed by os.fsync(f.fileno()).
>
> If only it were that simple. It has been documented that some disks will
> lie, even when told to sync. When I say "some", I mean *most*. There's
> probably nothing you can do about it, apart from not using that model or
> brand of disk, so you have to just live with the risk.

It's often close to that simple. With most hard disks, you can make
them 100% reliable, but you may have to check some disk parameters (on
Linux, that's just a matter of writing to something in /proc
somewhere, don't remember the details but it's easy to check). The
worst offenders I've met are SSDs...

> USB sticks are especially nasty. I've got quite a few USB thumb drives
> where the "write" light keeps flickering for anything up to five minutes
> after the OS reports that the drive has been unmounted and is safe to
> unplug. I corrupted the data on these quite a few times until I noticed
> the light. And let's not even mention the drives that have no light at
> all...

... but you've met worse.

> But my favourite example of lying hard drives of all time is this:
>
> http://blog.jitbit.com/2011/04/chinese-magic-drive.html
>
> I want one of those!

Awesome! It's the new version of DoubleSpace / DriveSpace!

http://en.wikipedia.org/wiki/DriveSpace

(And its problems, according to that Wikipedia article, actually had
the same root cause - write caching that the user wasn't aware of.
Great.)

ChrisA

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Thread

shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 11:12 -0700
  Re: shutil.copyfile is incomplete (truncated) Neil Cerutti <neilc@norwich.edu> - 2013-04-11 18:53 +0000
    Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 12:07 -0700
      Re: shutil.copyfile is incomplete (truncated) Neil Cerutti <neilc@norwich.edu> - 2013-04-11 19:55 +0000
        Re: shutil.copyfile is incomplete (truncated) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-12 00:06 +0000
          Re: shutil.copyfile is incomplete (truncated) Cameron Simpson <cs@zip.com.au> - 2013-04-12 11:15 +1000
          Re: shutil.copyfile is incomplete (truncated) Ned Deily <nad@acm.org> - 2013-04-11 18:33 -0700
            Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 23:32 -0700
              Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 23:53 -0700
                Re: shutil.copyfile is incomplete (truncated) Ned Deily <nad@acm.org> - 2013-04-12 00:53 -0700
              Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 23:53 -0700
              Re: shutil.copyfile is incomplete (truncated) Cameron Simpson <cs@zip.com.au> - 2013-04-12 18:26 +1000
                Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-12 02:18 -0700
                Re: shutil.copyfile is incomplete (truncated) Chris Angelico <rosuav@gmail.com> - 2013-04-12 19:22 +1000
                Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-12 05:07 -0700
                Re: shutil.copyfile is incomplete (truncated) Mark Lawrence <breamoreboy@yahoo.co.uk> - 2013-04-12 13:18 +0100
                Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-12 05:07 -0700
                Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-12 02:18 -0700
                Re: shutil.copyfile is incomplete (truncated) Roy Smith <roy@panix.com> - 2013-04-12 10:57 -0400
                Re: shutil.copyfile is incomplete (truncated) Roy Smith <roy@panix.com> - 2013-04-12 10:54 -0400
            Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 23:32 -0700
              Re: shutil.copyfile is incomplete (truncated) Roy Smith <roy@panix.com> - 2013-04-12 10:47 -0400
          Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 23:27 -0700
          Re: shutil.copyfile is incomplete (truncated) Roy Smith <roy@panix.com> - 2013-04-12 10:51 -0400
          Re: shutil.copyfile is incomplete (truncated) 88888 Dihedral <dihedral88888@googlemail.com> - 2013-04-12 08:49 -0700
          Re: shutil.copyfile is incomplete (truncated) Nobody <nobody@nowhere.com> - 2013-04-13 03:33 +0100
            Re: shutil.copyfile is incomplete (truncated) Chris Angelico <rosuav@gmail.com> - 2013-04-13 13:05 +1000
            [OT] Lying hard drives [was Re: shutil.copyfile is incomplete (truncated)] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-13 03:17 +0000
              Re: [OT] Lying hard drives [was Re: shutil.copyfile is incomplete (truncated)] Chris Angelico <rosuav@gmail.com> - 2013-04-13 13:43 +1000
        Re: shutil.copyfile is incomplete (truncated) Rob Schneider <rmschne@gmail.com> - 2013-04-11 23:25 -0700
          Re: shutil.copyfile is incomplete (truncated) Chris Angelico <rosuav@gmail.com> - 2013-04-12 17:32 +1000
          Re: shutil.copyfile is incomplete (truncated) Terry Jan Reedy <tjreedy@udel.edu> - 2013-04-12 10:48 -0400

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