USB device activity when not mounted

Polytropon freebsd at
Thu Jun 14 14:45:54 UTC 2012

On Thu, 14 Jun 2012 09:49:00 -0400 (EDT), Daniel Feenberg wrote:
> Is it possible that there is volitile memory buffering in the stick that 
> may not have been written to flash when umount thinks it is complete, and 
> the flashing light is an indication that power is still required to 
> complete the write to non-volitile memory?

That is possible, but then, the light should be silent
after a finite amount of time.

> Futhermore, are we sure that umount even waits for a sync? There is no 
> mention of that in the man page and I don't recall any long waits for 
> umount to return.

If I remember correctly, the umount command instructs the
kernel to write all pending file buffers and then detach
the device from the file system hierarchy. When the device
has been detached (doesn't appear anymore in mount output),
everything should have been written. However, as you said
it might be possible that _inside_ the USB stick there is
still an action that needs to be performed and therefore
requires power. But I doubt this takes several seconds to

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

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