Jerky video playback

[Ralf Mardorf]

On Wed, 2023-06-14 at 16:06 +0200, Volker Wysk wrote:
> Am Mittwoch, dem 14.06.2023 um 15:42 +0200 schrieb Ralf Mardorf via ubuntu-
> users:
> > On Wed, 2023-06-14 at 15:01 +0200, Volker Wysk wrote:
> > > There's another strange thing, which might or might not be related. I have
> > > two external hard disks, which I use for backups. Both have USB 3. When I
> > > synchronize the two, I get a data transfer rate which fluctuates between
> > > about 20 MB/s and 150 MB/s. That's what's displayed by the "rsync" command.
> > > I expect that this display is smoothed.
> > 
> > from hearsay it's what I would expect from shingled magnetic recording
> > (SMR) drives, see picture: 
> > https://www.researchgate.net/figure/Real-time-bandwidth-of-SMR-vs-CMR-disks-when-performing-random-writes_fig1_339923370
> > For visually impaired subscribers a description of the real-time
> > bandwidth of SMR vs. CMR disks when performing random writes. For CMR
> > drives it's more or less a flat line, while for SMR drives read:
> > https://www.musixmatch.com/lyrics/Vengaboys/Up-Down
> 
> That last link points to some music lyrics... You've posted the wrong link,
> have you?

No, it's just a joke. Bandwidth up and down and up and down ...

> I get the idea, what this shingled magnetic recording is (see Wikipedia).
> But I DON'T have many random writes. Most data is in a dozen or so of very
> large dar archives.
> 
> If it IS because of that SMR, then it's a weakness of the technology, not a
> (hardware) error, right?

Correct, that's my guess.

Even when syncing large files, it's a sync between two drives that
aren't empty, hence I would assume the worst. The drives aren't just
writing the new large files, they are also reading and rewriting several
layers of data of the same size the new files have got.

As long as I can get inexpensive CMR disks for backups I buy those. A
dedicated Toshiba series I often bought is migrating from CMR to SMR. My
dealer already sells some sizes as SMR only, while some other sizes are
still available as CMR, but in limited numbers.

What I will buy as soon as all inexpensive drives are SMR drives, will
depend on my financial situation.