[Discuss] full disk backups

[bogstad at pobox.com (Bill Bogstad)]

On Wed, Aug 21, 2019 at 1:39 PM Kent Borg <kentborg at borg.org> wrote:
>
> On 8/18/19 1:36 AM, Steve Litt wrote:
> > When I reformat my thumb drives as EXT4 they're much more reliable.
>
> Something I've noticed recently: When my link-dest rsync encrypted back
> up to a recent model USB-3 WD disk is done, unmounted, and ready to be
> unplugged...I can still feel it vibrating and doing something.
>
> I've decided this must be some useful housekeeping, and have waited
> until it quieted down.
>
> Anyone know what it is?

Guessing...

Can you tell if this is caused simply by the spindle rotating or are the heads
actively seeking?

If the drive has some kind of auto spindown after going unused for a while,
then it is likely to rotate for quite a while after you unmount it.  That may be
what you are seeing.  Unplugging it early shouldn't be a problem.

If it is actively seeking, that seems a little strange.   It is
unlikely that the drives
write cache can hold too much data.  Still it is possible that if the
final writes were
not contiguous, it might take a little while (maybe a second or two?).
Another thought is that
it might still be actively trying to remap bad blocks.   That could
take a while (multiple seconds?),
if it is having to retry.  If you aren't already monitoring the drive
for bad blocks (smartctl), you probably should.
It is harder to do on a USB drive; but if you fiddle with the right
options to the software, you can usually
make it work.  You really want to know if your backup drive is failing...

Good Luck,
Bill Bogstad