On Sun, 05 Aug 2018 11:38:11 +0000, Jan Panteltje wrote:

> On a sunny day (Sun, 5 Aug 2018 11:15:24 +0000 (UTC)) it happened Martin
> Gregorie  wrote in
> :
>
>>On Sun, 05 Aug 2018 08:25:34 +0000, Jan Panteltje wrote:
>>
>>> Yes, I have the old Unix habit of typing 'sync' 3 times every now and
>>> then.
>>>
>>> An other thing I notice with my USB sticks is that even after copy and
>>> sync the LED on the USB stick keeps flashing, sometimes for up to a
>>> minute or so.
>>> I once asked in a Linux group if it was safe to remove the USB stick
>>> when that LED was still flashing and was told that was OK...
>>> Nevertheless I always wait until it is off.
>>> For SDcards it is hard to tell, no LED, but I think the internal
>>> controller on the cards / sticks does some housekeeping even after the
>>> copy has finished.
>>> So maybe it is better to leave it in for a minute or so longer.
>>>
>>Its more important to *always* unmount the card before removing it, i.e.
>>click 'Unmount' on the card's icon if you're using a graphical file
>>manager or use the "umount"  command if you're working from the command
>>line.
>
> Indeed, of course only when it was mounted first :-)
> If you just copied _from_ an image umount is not needed.
>
> dd if=/dev/sd* of=myimage.iso does not need a mountg and umount.
>
>>The unmount process waits for any activities using the device to end,
>>makes sure any cached data is flushed to the device and disconnects it
>>when all related activities have ended. Do this for all removable
>>storage media, not just SD cards and USB sticks.
>>
>>NOTE that 'sync' just flushes cached data while 'umount' does quite a
>>lot more. 'umount' will not allow a device to be unmounted if:
>>- there are still files open on it - a process's working directory is on
>>it - it contains a swap file that's in use.
>
> Yes, the interesting thing is that even after umount the USB stick LED
> will flash for a while.
> Try it.

I can't try that: I have very few USB sticks and none of them have LED's
fitted. However, I'm not particularly surprised that activity would
continue because the USB controllers must be very small and low powered
and they have to deal with wear levelling some time and its a fairly safe
bet that it will have a lower priority than handling data transfer
requests.


--
Martin    | martin at
Gregorie  | gregorie dot org

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