Re: [gentoo-user] External hard drive and idle activity

[Rich Freeman]

On Thu, Jan 2, 2020 at 5:49 AM Dale <rdalek1967@×××××.com> wrote:
>
> lol  I didn't think of that and I don't recall anyone else thinking of
> it either.

That is because syncing before unmounting doesn't do anything.  Unless
you use --lazy umount blocks until all writes are complete to a
device.  The instant it returns as far as the kernel is concerned the
device should be safe to power off.

If you do a sync first then of course the umount will complete more
quickly, since all writes should already be flushed.

I have no idea what your device is doing after it is unmounted, but it
doesn't have anything to do with the linux kernel unless some process
is directly accessing the raw device (very unlikely).  Maybe the drive
firmware is doing some kind of housekeeping, or maybe the drive has
some kind of vibration in it that just makes it feel like it is doing
something.  Or maybe the NSA or Red Army has hacked your firmware and
it is doing who knows what (yes, the NSA bit at least is a thing).  In
any case, chances are the drive manufacturer has accounted for sudden
power loss in the design because if they didn't there would be a ton
of complaints, since there is nothing you can do about this sort of
thing assuming the firmware is up to something.

Out of curiosity, what model drive is it?  Is it by chance an SMR /
archive drive?  Due to the limitations on how those write data out I
could see them implementing an internal filesystem that journals
incoming data and then writes it back out after the fact.  If so then
that might happen even after the kernel thinks it is unmounted.
However, such a drive firmware would probably use a journal that
ensures data is safe even if power is cut mid-operation.  The drive
isn't supposed to report that a write is completed until it is
durable.

-- 
Rich