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I am planning to use four 2.5hdd's with a pi3 B. I plan to use four 'sata to usb y' cables, with each usb power leg of the y cables plugged into a powered usb hub and each data leg into each of the pi's four usb ports.

I was also considering powering the pi from the same hub using a usb to micro usb cable.

Here are the products;

Powered usb Hub

Y usb sata cable

Is this feasible? There doesn't seem to be much information on this particular setup even though I would have imagined it being pretty common.

My two main thoughts;

  1. If I use a usb to power the Pi from the hub, will the Voltage / Ampage be OK not to fry the pi?

  2. Will the read speed of each hdd drop the more hdds I add due to the pi usb controller?

  • provide 5V/2A to each SSD, though they can get by with less, being much less current-consuming that spinning drives. Get a 10A supply so you don’t get any surprises. Pi3B+ and earlier only give you a USB2 interface, you’ll never pull more than 480Mb/s for ethernet and USB ports combined. 60MB/s is still plenty unless you’re doing something special; reliable spinning 3.5in 7200rpm drives would usually yield 90MB/s. USB3+ is not necessary, just use the WiFi instead of wired networking. Configure a redundant RAID, or you will lose. – user2497 Mar 13 at 14:32
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Will the read speed of each hdd drop the more hdds I add due to the pi usb controller?

This is exactly what will happen. Connecting multiple HDDs (and the more so SSDs) to an RPi to increase disk throughput is a waste of effort. The RPi cannot transfer data faster than ~25 MB/s, no matter how many disks you connect to it.

I won't go into details regarding power consumption, but 4 HDDs plus an RPi will require the hub to provide up to 6 Amps, which is a problem for most of them. Like I said, you are better served by a single HDD (or a flash drive if you need fast random access).

  • That hub is 40W/8A but do you mean the Pi alone will require 6amps even if the hdds are powered externally? Disk throughput is not an issue for me, the Pi will act as a cheap media player and data-storage. – myol Mar 11 at 14:28
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    No, the RPi may take up to 2 A plus 1A per HDD, for a total of 6. Of course, if you have many disks you'd like to put to use, you can do what you described. Your question mentions SSDs, which is why I assumed that performance was important. – Dmitry Grigoryev Mar 11 at 15:36
  • @DmitryGrigoryev the performance requirement is not implicit, spinning disks lose their magnetic patters after ~5 years, while SSDs don’t. And there’s the noise. – user2497 Mar 14 at 0:58
  • @user2497 If you plan to rely on SSDs for long-term storage, you're in for a surprise: SSDs can lose data in as little as 7 days without power – Dmitry Grigoryev Mar 14 at 7:49
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    @user2497 7 days is of course an extreme case picked to make a flashy title, but in general you shouldn't expect data stored on an unpowered SSD to remain intact for more than a year or two, and HDDs are a better option for long-term storage. – Dmitry Grigoryev Mar 14 at 13:04
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Plan to provide 5V/2A to each SSD, though they can get by with less, being much less current-consuming that spinning drives. Get a 10A supply so you don’t get any surprises. You can use the same supply for the Pi, but power it via the microUSB port, not the 5V pins (2, 4), these aren’t protected by the polyfuse. If you do use this supply for a Pi, add a 10.000-20.000uF electrolytic reservoir cap on the 5V input. You can get by with 3.300uF if necessary, it is just to ensure no sudden increased current draw causes undervoltage. Many playerpimps use reservoir caps on the ‘woofers in the rear of their automobiles. But it was Milliways who taught me this lore! All hail!

Pi3B+ and earlier only give you a USB2 interface, and you’ll never be able to pull more than 480Mb/s for ethernet and USB ports combined. A nominal I/O of 60MB/s is still plenty unless you’re doing something special, e.g. video editing. For comparison, old and reliable spinning 3.5in 7200rpm drives will usually yield 90MB/s.

USB3+ is not necessary, just use the WiFi instead of wired networking. Configure a redundant RAID, or you will lose.

Note that you can get Mini PC (mini itx) PSUs with a 10A 5V rail (very stable, no voltage drop under load, will turn off if short-circuited, overheated, overloaded), these are always superior to weird little USB hub power supplies from god-only-knows. You just need to short a few wires, maybe add a dummy load to keep the PSU online. Google: pc power supply dummy load short — the thin wires are the ones you want to play with, but the wire colours do vary.

Edit: SSDs are useless, unless you can guarantee they are ‘continually refreshed’: From https://www.extremetech.com/computing/205382-ssds-can-lose-data-in-as-little-as-7-days-without-power : An enterprise [SSD] drive stored at 25C and operated at 40C has a retention rate of just 20 weeks. It was all too good to be true, SSDs are only for workstations and laptops/;

Good luck!

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