David Lethe wrote:
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USB for root??
Bad bad bad bad idea .. unless you get the industrial flash memory.  The
typical max number of writes for consumer-grade USB flashdrives is
around 25,000 ... but the low end of the range is 10,000 writes.  

Why do you think root filesystem will be written that often?
Here, / is mounted read-only..  And it changes only when you
change some configs...

So, root (and /usr) are ok for flash.  Just don't put /dev on it
(udev/whatever works), and don't put volatile filesystems like
/var there too.

/mjt