On Fri, 2021-06-18 at 09:02 -0300, George N. White III wrote:
> On Fri, 18 Jun 2021 at 06:50, Patrick O'Callaghan
> <pocallaghan@gmail.com>
> wrote:
>
> > On Fri, 2021-06-18 at 08:58 +1000, Cameron Simpson wrote:
> > > On 17Jun2021 12:15, Patrick O'Callaghan <pocallaghan@gmail.com>
> > > wrote:
> > > > On Thu, 2021-06-17 at 07:20 -0300, George N. White III wrote:
> > > > > > The technical specifications of the drives should mention
> > > > > > startup
> > > > > power
> > > > > management. There may also be some power management in the
> > > > > dock.
> > > > > I've noticed that it is becoming more difficult to find
> > > > > detailed
> > > > > documentation
> > > > > of add-on hardware. At one time you could open the box,
> > > > > identify
> > > > > key
> > > > > IC's
> > > > > and get the spec. sheets, but now you may find a general-
> > > > > purpose
> > > > > CPU.
> > > > >
> > > >
> > > > It's a cheap dock so probably not easy to find any technical
> > > > documentation. One thing I might try is to swap the two drives
> > > > around
> > > > just to see if it's always the same one that causes the delay.
> > >
> > > On the subject of power as raised by George, I had trouble with too
> > > many
> > > USB bus powered drives on the home server. A powered USB 3.1 hub
> > > helps
> > > me out there. Doubtless it has its own limits.
> >
> > The dock has its own power supply.
> >
>
> Is this a full-featured dock with USB and monitor outlets or a
> disk only dock?
>
> It might be useful to compare the rating of the power supply with
> the peak load from the drive spec sheet. Older high RPM drives
> had quite high startup draw. Does the power supply have multiple
> voltages or just one voltage (the latter requires conversion in the
> hub)? If the power supply can't meet the startup requirements of
> two drives then it must be doing some power management. The
> simplest approach would be to provide a delay before starting
> one of the drives.
Interesting idea. Mine is this model:
https://www.amazon.co.uk/gp/product/B06XYJGDTH/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
The power block says its output is 3A at 12V.
The drives are both WD model WD10EZEX, (though the label on one says it
has a 64MB cache and the other doesn't). Both labels say 5VDC, 0.68A
and 12VDC, 0.55A. Looks like the dock's power should be enough.
says 12V peak load is 2.5 A. It does take power to spin up to 7500 RPM, and I doubt your
supply could survive without staggered startup.
> Amazon has a popular Sabrent disk-only dock -- one review notes:
>
> Cons
> - when using 2 drives and plugging or unplugging one drive BOTH
> go offline, at least temporarily. NOTE: Seems to be a common limitation
> to all these docks. I have yet to find one that does not behave this
> way.
> Must be the way the SATA bus controller is designed.
> - when plugging in 2 drives, they mount sequentially, meaning you
> have to wait for one to mount before the other will
My problem is that one drive comes up almost instantly and the other
takes 30 seconds. In fact I can live with that. My real gripe is that
the kernel makes me wait even though the drive is not being accessed.
If it just wants to make the drive available, it should be able to wait
asynchronously.
Agreed, but then you need a way to tell the kernel that it won't need anything
from the external drives so it is OK to continue booting. Have you considered
automounting the drives?