That is interesting, I looked over all of my drives before I put them in and the bigger drives certainly seemed to have higher mA ratings - but am not going to pull them all out now to look again 
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From 10TB on, most drives are 7200rpm.
I would have expected those to draw more power.
So I installed and powered up the new hat.
https://www.waveshare.com/usb-3.2-gen1-hub-hat.htm
No luck. I could see 8 out of 13 drives and that’s it. I did order the transparent 7 port unpowered hub as mentioned earlier. We’ll see if that works, but at this point I’m assuming my Pi is faulty?
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I am sitting at 21 drives:
However, my hubs or my Pi is starting to act up now. When I passed the 20 drives mark, 2 of my drives did disappear. I had to disconnect and reconnect the disappeared drives. Nonetheless, they show up without any issue.
I also checked my plots’ response time with chia plots check. It took around 4 secs no wonder chiadog didn’t inform me about any response time issue:
I am suspecting Chia’s GUI that it could take a troll on my CPU when farming on many drives as my CPU is running at above 90% all the time now:
I will farm with chia start farmer-no-wallet but I am not sure yet that could allow farm without having to sync the full node. If that works, it would significantly reduce the CPU usage.
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I ordered another Pi 4 from a different vendor. Going to see if that works. If not, I’m going to go with a cheaper NUC running Linux.
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4 seconds is a lot
I wouldnt dare to get that near to 5s.
But I didnt plan to go over 8 drives per pi anyway.
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Is it the same drives that don’t show? Could be a compatibility problem with the USB->SATA adapters.
You know what you need?
A powered USB hub. 
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Hi, I’m new to this business. Can you please tell me which Pi 4 is better for farming? 4gb or 8gb memory? I also read carefully. I’m wondering what the maximum load 1 board can carry. What kind of hat to take or not, etc.
You better have the 8GB model. It’s essential to have 8GB RAM as you can disable swapfile completely making your Pi a lot faster, especially when you install the OS on a microSD card. You can’t do this with the 4GB model.
As for the maximum load (maximum USB drives connected), I’m still testing this myself 
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Pretty interesting. I will wait for the results of your experiments. I ordered myself a Pi4 8gb. Does it make sense to install any hats? Or are there enough hubs? How many megabytes can 1 access consume? It is possible to calculate to roughly understand how many hard drives are enough for 1 usb 3.0 port
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I don’t think it makes sense to install any hat if all you want is USB hubs. The USB hub hat uses the VL817 controller chip which could be found on many USB hubs. Therefore it makes more sense to go for a cooling solution rather than the hat considering that running Chia’s GUI is quite hard on the Pi CPU:
My CPU is running at 70 C ++ all the time with the official heatsink and fan attached.
How many megabytes can 1 access consume? It is possible to calculate to roughly understand how many hard drives are enough for 1 usb 3.0 port
The Pi uses VL805 as its USB host controller chip. Therefore I don’t think it will have a different limitation than your typical PC. As long as it does not exceed the 5Gbps that the USB 3.0 host supported, it should work fine.
However, I am facing a problem when I went above 21 drives. When I connected the 22nd drive, no matter what I tried, the 22nd drive didn’t show up. That’s with the unpowered hubs. I am waiting for my powered hub and I will report back again whether I can go above 21 drives.
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I am here, I am not sleeping, I wonder. I have a 16-port powered hub and it’s plug and play. It is interesting to know the limit. Do you think water cooling is more than just fun for Pi?
upd1:
Can you specify the model of your SD card? And if you can link to the product or its description. So that I can pick exactly what you have tested. Thank you. And why did you decide to take the Pro version? Does it handle more rewriting cycles?
upd2:
CPU load without GUI? Does it make sense in this case to add a second Pi and it is possible to increase them as a cluster? If we find the optimal value for 1 individual board (number of disks + stable CPU temperature) And again, what is the recommended temperature for the Pi.
upd3:
I’m wondering how much of the usb channel is consumed by one blockchain call. When the check is in progress. Is it possible to proceed from this? Or is it not reasonable.
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Testing The Water Cooled Pi
I think water cooling is fine for us. You can connect several Pi to one pump at once
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This is normal and expected. The Pi 4 has 30 available device address slots. You have 21 drives and 3x 7-port hubs which each use 2 controller chips chained together, each of these counts as a device.
21 drives + 6 controller chips (from 3x 7-port hubs) = 27 devices.
It varies based on how the USB hub is designed, but in your case each hub may count as a device too, adding another 3 devices = 30 in total.
As you noted earlier, powered hubs are not usually required if you have externally powered drives, and won’t enable more devices in this case because of the device address limit. Plus there is the backfeed issue.
Source:
https://www.raspberrypi.org/forums/viewtopic.php?t=255156
EDIT: correction to the number of controller chips (it depends on the hub design).
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Thanks for the info. I think I need another Pi now
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Most likely! Try running lsusb -t and count the number of entries.
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A simple lsusb | wc -l should give you the count of devices/used addresses.
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Now you have a decision to make, upgrade your pi or get a second pi as a harvester.
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Hello, short time listener, first time caller …
I have a powered hub, 3 enclosures with lets say 12 drives and a couple other SSD’s attached so lets say 15 drives. not having an issue addressing the drives and getting them mounted.
I am having issues with throughput and general USB hub reliability. Inconsistent behavior plugging the keyboard into the USB3 hub. I gave up trying to copy a plot across it. If I need to copy a plot to top off , I plug the source into usb2 port and send it to the destination usb3 port. Today, very concerning, I was doing a plot check against everything and all the drives spontaneously unmounted, the OS did not see anything on that USB3 port / hub. Reboot fixed. Im fine with having a remote harvester to plug drives into but starting to feel the Pi is a weak link .
Common issue or a flaky hub?
Thanks for taking my call.