In the SATA thread comment was made about older drives being "too small"
While at first thought we had some of this  already worked out- a new angle comes up.

The concept of older smaller drives being used as  "in place failure mitigation"

Overview is: A fully functional install with minimal yet complete tools for recovery.
However the functionality has to include daily use items such as web browser,light office etc.
The real shining grace comes when drive appearing to windows as letter R or similar saves the day.
That day saving is executed by having copies of the most recent user data- and tools to use it.
Or at minimum burn/network/email a copy of that user data. So how is this concept different?

THIS concept boots up to a stable Linux desktop and turns panic into hope.
 Boot sequence  is set so a primary drive boot failure invokes the "recovery drive" to take over. Allowing recovery in a graceful no panic fashion. Even possibly showing a Windows user how
Linux can save the day.