mindwave
Posts: 36
Joined: Mon Aug 29, 2011 5:24 pm
Contact: Website

MAX NUMBER OF USB HD's

Thu Jan 11, 2018 5:34 pm

Team,

Benn a sole Linux guy for 15 years. Only reason I even have a win10 pc in the house is my sons school requires he have access to what they have.

However over the past few years I find myself running into an issue no matter what Im dealing with.
1) I have 1/2 dozen pi's in the 2 through the range. and now my boy is at that point, I want him continuing to excel so now that hes taking his 1st computer class, hes going to build his 1st PC
2)I have a spare PI ready for this project. as well as everything else he needs, mouse kbd, external storage 22" and 10" monitors, nics etc
3) my main pc is an 8 core AMD w/ 32+ GB of ram about 35TB of HD space inside and another dozen 1TB-4TB hd's wating outside the box

On my desktop, I seem to be able to plug in no more that 4 external USB2 or USB3 ports, PLUS I have a fully powered 7 ports for the whole power strip. I plug in drive 5 and either rit wont load OR it will drop off and take something else w/ it.

Clearer example: I have 4 4TB USB Drives ready to go, I power up the power strip, and plug in drive 1 - it appears and is ready to go. ditto drive 2,3 and 4.
But I have ANOTHER USB drive I want to get access to, so I plug it into the strip.
1) the drive NEVER appears
2)while waiting I power ip the next USB drive I plug it in.
- USB discovery never finds it
- I open RCS or SPACEFM or DOLPHIN, and I direct to the MEDIA dir and its not there
- lusb, nada, same w/ dmesg and fdisk -l
3) within about 60 seconds one of my other USBDRIVES will "drop off", NORMALLY its the "last on the list"
Im not terribly creative w/ naming so its USBHDD1 to USBHDD5, most recently its been the ones ;

On my RASPI 3 w/ STRETCH the newest drive never shows and it too will end up taking one with it.

Now all these drives have nice big in line buffers, so the line is clean, and powerd, the HUB allows me to plug in mice, trackballs Kinects. keyboards, mice,trackballs, IRigs you name it, and nothing ever shows in RASPI

is there like a 3 drive limit that ium not reading about?

I apologize for my typing rediculoulesly tired,

Thanks for any and all your help

mindwave
Posts: 36
Joined: Mon Aug 29, 2011 5:24 pm
Contact: Website

Re: MAX NUMBER OF USB HD's

Thu Jan 11, 2018 6:32 pm

PS., In reference to the drives Im wanting to use with the RASPI one is formatted EXT4 (that's the 4TB one)

one is NTFS that's the 3TB one then I have a VFAT 1TB drive.

Thanks
j

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HawaiianPi
Posts: 5969
Joined: Mon Apr 08, 2013 4:53 am
Location: Aloha, Oregon USA

Re: MAX NUMBER OF USB HD's

Thu Jan 11, 2018 8:05 pm

There is a limit of 127 USB devices, but there was a bug in Windows that caused trouble with more than 16 devices attached (and hubs count as devices). Microsoft blamed the drivers, and the chipset makers blamed Microsoft, so I don't know if that bug ever really got fixed. However, from your post it would seem unlikely this is your problem (you don't have that many devices, and you're running Linux).

The number of connected USB hard drives could be limited by power, and having a powered 7 port USB hub might not solve that, as many USB hubs with more than 4 ports do not come with adequate power supplies. If your external hard drives are self-powered, then they should work, but if you are using portable, USB powered hard drives, then you may be running into power problems (the fact that connecting extra drives also takes previously working drives offline suggests power issues).

The USB 2.0 spec is 500mA per port, so a 7-port USB 2.0 hub should have at least a 5V/3.5A power supply, and preferably a bit more (since there is no such thing as 100% efficiency), but many 7-port USB 2.0 hubs only come with a 2A supply (and even replacing that with a stronger PSU might not help, based on my experience with an old D-Link 7-port hub I have).

The USB 3.0 spec is 900mA per port, so a 7-port USB 3.0 hub should have a PSU that supplies 32W or more.

The Raspberry Pi models B+, 2B and 3B can supply up to 1.2A total for all 4 USB ports, with no per-port limits, but that is less than the 500mA per port of the USB 2.0 specification (1200mA/4 ports=300mA per port), so powering even 2 portable USB hard drives on a Pi can be problematic. An adequately powered USB 2.0 hub will usually fix that.

Another potential problem on the Raspberry Pi could be the hub itself, if you are using a USB 3.0 hub. Some USB 3.0 hubs are software devices that don't have a controller chip, and those will often only work on Windows/Mac OS. For the Pi it's best to stick with USB 2.0 hubs, or ensure that you have a hardware USB 3.0 hub.

And finally, for non Linux filesystem drives (NTFS/exFAT), make sure you have the appropriate drivers installed (ntfs-3g/exfat-fuse).
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