[PLUG-TALK] A computer for external storage?

Aaron Burt aaron at bavariati.org
Thu Oct 1 14:59:45 UTC 2020


On 2020-09-30 17:16, John Jason Jordan wrote:
<snip>
> I need my four drives to be in a RAID0 array, and to appear as external
> storage via Thunderbolt 3 on my Thinkpad. So I could just buy a
> motherboard with a TB3 port, put it in a cheap case, stick one of the
> four-port cards in it, and mount the drives in the drive cage. Of
> course, I'd need a CPU and some RAM, but the total could come to under
> $1000. And that's about how much the enclosure I was trying to buy
> costs. Plus, I could get the parts in a few days.
> 
> The problem that I can't figure out is what will happen when I connect
> a TB3 cable from my Thinkpad to the motherboard in the new computer? My
> intuition tells me that it would never work. Or I might end up with a
> pile of smoking U.2 drives.

That is a fun and educational problem to research. From what I can tell, 
the answer is "no damage would occur, but it won't do what you want."

Starting with Thunderbolt:  It's not ummm...gendered.  The cables cross 
everything over, so you can safely connect a computer to another 
computer, or a device to another device just as safely as a computer to 
a device.  While it can use up to 18 Volts, a cross-connection won't 
lead to burnination.

You can connect computers over Thunderbolt for networking.  Linux (and 
Windows) support Apple's ThunderboltIP protocol so you can have a 10Gbps 
connection without any extra hardware.

However, you want the computer to act like a disk, or in jargon, for 
Linux to act as a SCSI target over the Thunderbolt 3 fabric.  The 
Linux-IO Target (LIO) can do that over several other fabrics such as 
FireWire or Ethernet, but not Thunderbolt.

Confusingly, Apple devices support "target mode" over Lightning, but 
it's a proprietary thing that nobody else can talk to.

I don't know what you'll be doing with your 
Lamborghini-crossed-with-a-Mack-truck storage array, but if the 
immediate gathering/processing work can be done on a server instead of 
on your ThinkPad, you could build a little tower server for now and move 
the SSDs to a TB device later.

Also, hello!  I'm so glad that you're sounding well and I hope we get to 
talk in person again some day soon.

Regards,
   Aaron



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