Is it safe to unplug a blinking USB drive after 'safely' ejecting it?

Solution 1:

Usually it is, do what the user manual says

If the drive's firmware is written correctly, it announces to Windows that it's ready to be ejected when it is. It is therefore safe to do so.

If the drive's firmware is written incorrectly, it may announce that it's ready to be ejected while still busy with important stuff. It's therefore not safe to eject it, but then, it is never truly safe to eject (or do anything else) with a drive which has a buggy firmware.

For instance, here is a random HDD manual which says:

1. Click the “Hardware and Eject Media – icon” A pop-up message box will appear listing the external devices connected to your computer.
2. Select the TOSHIBA drive to eject. After a few seconds, you will get the notification that it is now safe to remove the device.
3. Click “OK” and you can unplug the drive now.

Note there's no mention of LED activity. Indeed you should check the manual of your drive, and if it says "wait for the LED to blink out EJECT in Morse code", you should absolutely do that. I'm yet to see such a manual though.

If you absolutely need your data to be there, verify the integrity of the data you have written, and make backups. Otherwise, when your data on a portable HDD is gone, the fact that you have waited until the LED blinks ten times will be of little consolation.

Solution 2:

I haven't seen any official source that describes the reason for blinking disk indicator after Safely remove, so what I write here is only based on general knowledge and observation. This happens for some disks because of the way that the firmware interacts with the operating system.

Windows announces that the device is safe to remove once it has flushed all its data from the memory cache and signaled the device's firmware to spin down.

The firmware itself may take some time to process the spin down command. Many USB hard drives also incorporate cache memory that will be lost if the disk is brutally powered down. The firmware will need its own time to terminate all writes and to spin down the disk. While it is doing that, the disk's indicator will blink.

It is certainly not safe to unplug the disk and power it down while the lights are blinking, since they indicate that the firmware is actively doing something. Some disks can recover from an abrupt power down by using non-volatile cache memory, so they can pick up when the disk is powered up from where they stopped.

Beginning from Windows 10 version 1809, it is safe to unplug the disk whenever the disk is not blinking. Safely remove is no longer strictly necessary, although I would still recommend it.

Solution 3:

Data is only guaranteed safe when electrical activity of external drive has stopped. Blinking shows that the external drive is still receiving electric power from the computer, therefore we cannot be sure that some data operation will not happen.

In Linux this is easy to make sure, because unmount and detach are two separate stages:

udisks --unmount /dev/sdb1 ..LED on, power ON

udisks --detach /dev/sdb ..LED off, power OFF

Windows does not have Power Off command but only Eject, which is similar to unmount, therefore in Windows in some cases it might be better to shutdown the whole computer as that guarantees that the external drive is also free of electric power.