Parkour_Lama
Posts: 17
Joined: Fri Jun 12, 2020 6:29 pm

Double Check, Power Requirments

Thu Jun 17, 2021 7:40 pm

Hello mates,
I've been running a single 2.5'' HDD for quite a while now on my Raspberry Pi 3B+.
Works great, power and data are handled though the USB 2.0 connection.

Now, I want to add another 2.5'' HDD.
Well, I tried plugging it straight in, the Pi didn't like that and reset itself every few seconds.
Looks like I'm gonna have to get an external Powered USB Hub?

Now, I know a few things, but my basics are shaky and I wanted to run this by someone who knows their stuff.

1. My first HDD is a WD Scorpio Blue.
Rated at 0.7 - 1.3 W with a peak of 2.6 W, I've got a Y - shaped USB splitter (refer images)

Image

So the thick ends will connect to the Pi and HDD, while the thinner one to the dock, with the Pi on the dual cable end, correct?

2. The second HDD is a Toshiba Backup Drive.
It claims to be rated at 900mA, so 4.5W usage? Probably a tad more at max.
This one is a bit different.
Currently off my laptop the setup was:

Image

This worked fine, but isn't for the Pi.
So I found this:

Image

Is this really what I need?
I've only found one seller, than too sold out, I expected it to be more widespread.
If anyone's got a better idea, I'm more than welcome :)

klricks
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Location: Grants Pass, OR, USA
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Re: Double Check, Power Requirments

Thu Jun 17, 2021 8:01 pm

The combined total power output of all 4 USB ports is limited to 1.2A. In general from many other posts here, you won't be able to run more than one 'spinning rust' HDD. A 'Y' splitter will not help.
You would need to add a powered USB hub.
Last edited by klricks on Thu Jun 17, 2021 8:06 pm, edited 1 time in total.
Unless specified otherwise my response is based on the latest and fully updated RPiOS Buster w/ Desktop OS.

Parkour_Lama
Posts: 17
Joined: Fri Jun 12, 2020 6:29 pm

Re: Double Check, Power Requirments

Thu Jun 17, 2021 8:06 pm

klricks wrote:
Thu Jun 17, 2021 8:01 pm
(Unless you add a powered USB hub.
Oh yes, perhaps I didn't make it clear enough.
All these cables will be plugged into a powered USB hub, with only data lines running to the Pi.

LTolledo
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Location: Anime Heartland

Re: Double Check, Power Requirments

Thu Jun 17, 2021 9:31 pm

my RPi3B+ desktop with 3 HDDs
RPi3B+ 4port USB3hub 2drive copy full view.jpg
RPi3B+ 4port USB3hub 2drive copy full view.jpg (197.08 KiB) Viewed 224 times

one HDD is in the acrylic case with the RPi3B+
two other HDDs connected to the RPi via powered USB hub
on this test I was doing directory copy between the USB hub connected HDDs...
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

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HawaiianPi
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Location: Aloha, Oregon USA

Re: Double Check, Power Requirments

Fri Jun 18, 2021 12:56 am

Short Answer
USB Y-Cables with an extra power plug won't help in a Pi, and likely won't help on a hub. What you want is an enclosure, dock or hub that will power the drives without back-powering the Pi.


Long Answer
Common Windows and Mac OS computers usually follow the USB power spec and supply 500mA per USB 2.0 port and 900mA per USB 3.0 port (or more). Pi computers are different because the SoC only has a single USB 2.0 interface, with additional ports derived from either an on-board USB 2.0 hub chip (1B to 3B+ models) or a PCIe to USB 3.0 controller chip (4B).

Pi models with four USB type-A ports (B+ to 4B) have a total current of 1.2A available with no per-port limits (in other words, all 1.2A can come from a single USB port if it's the only one in use). For a single port this exceeds the USB 3.0 (900mA) power spec, but it should be obvious that when you start using other USB ports that won't necessarily hold true (2x900mA USB 3.0 drives would require 1.8A).

As someone else mentioned, using Y-type USB cables with an extra power plug doesn't help on a Pi because there isn't any additional power available from other ports. On a hub it may or may-not help, depending on the hub and if it has per-port power limits (many don't). Also, it's not uncommon for hubs to be under-powered (I've seen a lot of 7 or 10 port hubs with only a 5V/2A PSU, which isn't even close to enough). Hubs may also back-power a Pi, but that's another problem and discussion.

The best solution is to use self-powered drives that don't require power from the Pi. Multi-drive docks are another option that I've had good luck with. Powered hubs that don't back-power (and have a sufficiently large PSU) would be great, but finding those can be difficult (some here have resorted to cutting the power wires in the USB hub/dock cable going into the Pi to resolve back-powering issues).
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?

Parkour_Lama
Posts: 17
Joined: Fri Jun 12, 2020 6:29 pm

Re: Double Check, Power Requirments

Fri Jun 18, 2021 6:13 am

HawaiianPi wrote:
Fri Jun 18, 2021 12:56 am
Short Answer
USB Y-Cables with an extra power plug won't help in a Pi, and likely won't help on a hub. What you want is an enclosure, dock or hub that will power the drives without back-powering the Pi.
I've read both the answers, and they're quite useful.
It's a shame plugging into a dock won't work, I was hinging on that idea.

Nevertheless, do you have a photo/link to an example?
Looking it up, all I seem to find are enclosures that convert SATA to USB, via a single cable, so data and power simultaneously, or large and expensive docks for multiple HDD's.

A powered USB hub seems to be the best course of action right now.

Parkour_Lama
Posts: 17
Joined: Fri Jun 12, 2020 6:29 pm

Re: Double Check, Power Requirments

Fri Jun 18, 2021 6:15 am

LTolledo wrote:
Thu Jun 17, 2021 9:31 pm
my RPi3B+ desktop with 3 HDDs
RPi3B+ 4port USB3hub 2drive copy full view.jpg
Quick question, even though the hub might be USB 3.0, the ports on the raspberry Pi are still USB 2.0, so doesn't that throttle performance when you've got multiple drives in the Hub?

LTolledo
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Location: Anime Heartland

Re: Double Check, Power Requirments

Fri Jun 18, 2021 9:13 am

from that directory copy activity....
82.1GB completed transfer in 2hrs...
"Don't come to me with 'issues' for I don't know how to deal with those
Come to me with 'problems' and I'll help you find solutions"

Some people be like:
"Help me! Am drowning! But dont you dare touch me nor come near me!"

Parkour_Lama
Posts: 17
Joined: Fri Jun 12, 2020 6:29 pm

Re: Double Check, Power Requirments

Fri Jun 18, 2021 9:43 am

According to my calculations, you're averaging at roughly 11.67 (12) MB/s.
My benchmarks on a single disk are around 24 MB/s.

So roughly half of the expected speeds.
The Pi should be able to support all 4 drives at the theoretical 30 MB/s, if each were plugged seperately.
Or are there limitations I'm unaware of?

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