[Bug 1681138] Re: silent file corruption with cp -ar file transfers to USB

[Pádraig Brady]

What's the nature of the corruption? For example is there too little data?
How do you mean "flush of the write buffer"?
3 seconds sounds way too short to actually write the data.
I presume you're unmounting the device before ejecting it?
Note cp is just doing read/write so unlikely to be the issue.
Note also cp reads/writes 128KiB at a time,
whereas dd defaults to only 512B at a time and so may avoid async issues.

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https://bugs.launchpad.net/bugs/1681138

Title:
  silent file corruption with cp -ar file transfers to USB

Status in coreutils package in Ubuntu:
  New

Bug description:
  The OS is 16.10 Yakkety LiveCD.

  I'm seeing silent file corruption when using the cp -ar switches for
  file transfers to a Sandisk Ultra USB 3.0 32GB thumb drive across a
  USB 2.0 bus.

  The first indication of a problem is when attempting to read the data
  at some point in time after the initial copy.

  The copy command completes successfully with no visible errors.

  At first I thought this may have been related to an async write,
  however; the issue persists after a flush of the write buffer prior to
  ejection of the device, and there are no issues with DD.

  As a test, a 2.5G file was generated with random data and then copied
  with cp -ar to and from the device. The copy completes with no visible
  errors within 3 seconds.

  I've included the strace log of the transfer in action as an
  attachment.

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