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I have a Pi 3B+ which I'm using as a home media server - it has been connected to an old 2TB Seagate HDD (with its own external power supply) for a couple of years and running openmediavault software. It worked nicely until yesterday - suddenly lots of errors when accessing the HDD and it's making strange noises.

Seems highly likely that the HDD is dying, so yesterday I went to Amazon and ordered a 2TB Samsung 870 QVO SSD (2.5" internal drive type), and a SATA to USB adapter. They should arrive today.

However...will the power supplied by the Pi 3's USB ports be enough to get it working without a separate power supply? I've read that the USB ports are good for 1.1A @ 5V so that's 5.5W, and the power consumption of the SSD is supposedly about 4W - but does the SATA to USB adapter use a bit of power as well? Unsure if it'll work.

Electricity is quite expensive here in the UK so I'm keen to have a setup that uses as little power as possible (because I run the Pi server 24/7). Speed is less important to me than low power consumption in this situation.

If the Samsung won't work, is there a different SSD that anyone could recommend as having a better chance of success? Alternatively, would I be better off using an NVME drive instead? I don't suppose I'll get to see its full speed potential in this setting, but that's not important, and I might redeploy it in future anyway, inside the new desktop PC that I'm quite likely to buy in the next 12 months.

Thank you.

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    I have all of my Pi 4's using various and many SSD drives over USB ... never had an issue Commented Nov 9, 2023 at 9:56

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Your question is a two-part question:

  1. how much power does my SSD require?
  2. how much power can the RPi 3B+ source through one of its USB ports?
Re Question 1:

The Samsung-provided power requirements for your 2TB Samsung 870 QVO SSD are a bit ambiguous. The table in this document lists power consumption figures for the 2TB unit in Active Mode at 2.2W-2.5W. However, another Samsung document lists the power consumption at 2.1W-3.0W (Read/Write=active) for the 2TB unit. So much for truth in advertising. :)

You also asked about power consumption of the USB-SATA adapter. Yes, as with all electronics, it does consume power. The active component in most USB-SATA adapters is a USB-SATA bridge chip: e.g. the TI TUSB9261, or JM20329. According to the TI spec sheet, the bridge itself will consume about 5 uA (i.e. negligible power). There are also voltage regulators for converting the 5V USB to 3.3V used for SATA, but their burden to the power consumption will be limited to the in-efficiency of the regulators. We can estimate that at 10% of the max 6 W - or about 0.6W.

Based on the mfr documentation discrepancy, I would be inclined to say that the worst-case estimate for power required by the 2TB Samsung 870 QVO SSD is: 3.0W. The adapter is estimated (very conservatively) to consume 0.6W - or 120 mA. And so, at 5V (perhaps a bit more), this works out to approximately 3.6W, or 720mA.

Re Question 2:

There have been many questions (here in RPi SE and in the RPi forums) regarding the USB power capacity. Reviewing some of these Q&A indicates that USB power capacity seems to have changed over time, and across RPi models. This makes a definitive answer... challenging. Also, the RPi hardware (and firmware) design is proprietary; this also adds a bit of uncertainty.

Consequently, the best (most reliable) source of information and specifications on RPi is in the documentation provided by the manufacturer. With respect to USB power capacity, the manufacturer's documentation is here - listed in the table under the column 'Maximum total USB peripheral current draw'.

The only remaining ambiguity here is how the mfr-quoted USB power capacity applies to a single USB port - since your adapter will plug into only one port - not all 4. I've read somewhere that the total USB power capacity can all be sourced from a single port. This is consistent with the way USB hubs are designed.

For the RPi 3B+, the table states the USB power capacity is: 1.2A At 5V (perhaps a bit more), this works out to approximately 6W. This of course assumes that the Pi's power supply meets specifications (5V, 2.5A).

Answer:

Yes, the power supplied by the Pi 3B+'s USB ports will be enough to run your 2TB Samsung 870 QVO SSD without a separate power supply.

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  • Thank you very much indeed. I've been able to get the disk working in the last 30 minutes, and yes, it seems to be fine so far. However I'm getting occasional low voltage warnings from the Pi's command line. This isn't new though, and I was seeing them before I connected the Samsung drive. However I'm using a cheap and nasty power supply - perhaps I should invest in the official one to see if that fixes the problem. The low voltage warning isn't interfering with the Pi's operation as far as I can tell, however.
    – Alan
    Commented Nov 9, 2023 at 18:03
  • You are welcome - glad it helped. And yeah - I didn't believe in investing in the "official" pwr supply for years, but I've come around to it. It doesn't completely stop the low voltage warnings, but greatly reduces them.
    – Seamus
    Commented Nov 9, 2023 at 19:46

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