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

[Nathan]

>What's the nature of the corruption

Its unclear, file attributes, names, size all appear the same from ls output.
I initially discovered it while setting up a local repo, dpkg didn't recognize the deb file output. 
Diff throws IO errors. 
Copying with cp appears to work (failing silently)
dd & rsync both throw an input output error when attempting to copy affected files.
lsof of the affected files directly after a copy throws an unable to stat (I'm not too versed with lsof so that may be a common problem unrelated).

>How do you mean "flush of the write buffer"?

I used hdparm -f on the device node after unmounting it, I then used
eject before physically removing it.

>3 Seconds sounds way too short -
My thoughts exactly, the copy was over a usb 2.0 root hub so I would expect no more than 30MB/sec.

The issue only appears for this specific USB Drive I've tested 5 other
usb thumbdrive models with no issue.

I've linked the exact model below.
https://www.amazon.com/SanDisk-Ultra-Transfer-Speeds-s-SDCZ48-032G-UAM46/dp/B00KYK2AKO

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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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