df shows negative bytes used.... only during dd

Asked Jul 26 '21 at 13:20

Active Jul 26 '21 at 13:20

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I have begun a dd to copy a partition on one usb drive, to a 2nd usb drive. While I have freshly reformatted the destination partition (/dev/sdc1), and it checks out with fsck normally and shows it is empty with no issues in df, like this:

Filesystem      1K-blocks       Used  Available Use% Mounted on
/dev/sdc1      1536927656      77852 1458708416   1% /media/test/WD4

as soon as I start the dd, it shows negative values in df:

/dev/sdc1      1510427560  -26422244 1460033420    - /media/test/WD4

Is this a correct behaviour during dd? It's approximately 1 Tb to transfer over USB and will run for over 12 hours, but if something is wrong I don't want to have to wait all that time to find out.

asked Jul 26 '21 at 13:20

J B

Looks like corruption. Maybe you've got a bad drive? – Michael Hampton Jul 26 '21 at 13:36
suspiciously cheap 1 TB USB drive? – Simon Richter Jul 26 '21 at 13:52
Yes, it was suspiciously cheap... but it's western digital, and I just assumed all usb drives were insanely cheap these days! alright I can dig into the drive a bit further and try to tease out some problem with it. – J B Jul 26 '21 at 14:20
1

Well, turned out to be a simple oversight. I hadn't unmounted the target partition. – J B Jul 27 '21 at 13:05

df shows negative bytes used.... only during dd

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