On Sun, 17 Apr 2016 10:47:55 -0400, "Robert P. J. Day" said:
i figure this is as good a place as any to ask ... is anyone here aware of anyone using a linux config and install that, for the purposes of reliability or high availability or whatever you want to call it, relies on a second, completely independent installation of linux on the same hard drive?
IBM's AIX has for a long time had the concept of an 'alternate boot volume', which can be another logical volume on the same physical hard drive. But it's not intended for high-availability, it's for "if this software upgrade goes pear-shaped I have an easy backout procedure". And it avoids most of the "you have to keep two version" issues by providing a tool to copy your *current* system onto the alternate boot. I'm sure some Linux distros have stolen the concept. Most implementations of "high availability" would see the phrase "on the same hard drive" and start pointing and laughing at the single point of failure.