it takes time to go up to full speed

I have the same problem with the Rpi.
How stable is the setup?
it runs the whole day today, without problems

but as i said hash rate a bit lower than on my desktop pc.
I have to build a case for the configuration, then it could run 24/7. Until that it only runs ~12 hours a day.
I'm using a noname usb stick with 1GB storage. are there many reading operations to the stick?
Or maybe the usb hub sucks, because it's a cheap hub.