Good luck 
if ever your install does weird things at some point tell yourself it’s not Gladys
Hello @Jean34,
What case do you have for your SSD?
I have this one: Inateck Boîtier de Disque Dur Externe USB 3.0 pour Disque Dur Externe 2,5" SATA HDD et SSD, Prise en Charge UASP, sans Outils,FE2013 : Amazon.fr: Informatique
But I can’t get the Pi to start.
The Pi is well configured because I was able to boot from the USB key.
I have a Pi 3B+ and the case is USB 3, maybe that’s why, right?
No, that’s not it, even if the ports are not USB3, it works (in USB2 mode)
Hello,
What are you actually trying to do? It’s a bit confusing… From what I understand, you’ve sent the image of your USB key to your SSD?
I abandoned the USB key, and I’m testing to use an SSD, it’s a new image.
@VonOx, I suspected as much.
I think more for the case, there is an on/off button on it. Is this a problem?
Have you tried the software that Vonox provides in another discussion? Apparently, you can directly choose to install on an SSD
This could also be due to the case not having a power supply, so it draws power from the Raspberry Pi and it may not be sufficient
I will try.
What case do you have for your SSD?
I haven’t migrated Gladys to SSD yet, due to lack of time.
It’s an adapter that I have 
The case I mentioned earlier, I ordered it for someone and I don’t think it turns on automatically, we should also check that side
Hi @Tlse-vins,
For my part, I have 3 like this: https://www.amazon.fr/dp/B07D2BHVBD?ref=ppx_pop_mob_ap_share
For 3 Gladys and they work very well. I had a low-end one before at €12, it never worked, with 3 different SSDs.
@Terdious he has a Gladys cluster 
You should check if you can bypass your on/off button so that the box turns on directly when it is powered
Not much of a choice, need user security and MultiDashboard ^^ 
So to sum up:
- Do not use a cheap or no-name USB key as the data is quickly corrupted.
- Do not use an SSD with a button.
This one works very well:
So in the end… 
No installation on USB key 