Moving from EL N to EL N+1

[Yasha Karant]

Rather than hijacking the thread on vlc, I am posing this as a new set 
of questions.

My understanding of the EL upgrade process, when moving from EL N to EL 
N+1 (e.g. EL 5.7 to EL 6.1), there are only two ways to protect the 
information on the hard drives that have "systems" directories (e.g., / 
, /boot , /usr , ... ).

1.  Make backups of everything and restore after the EL N+1 installer 
runs, hopefully forgetting nothing of importance.

2.  Keep /home , /opt , /usr/local , and all other non-distribution 
given applications, configurations, and data, on separate partitions 
that are not touched during the EL N+1 installation process by using a 
manual override selection during the EL N+1 installation process.

2.1  If these are not real partitions but are handled via the Linux LVM 
method, will these be respected or will these be overwritten?

2.2  Is there any mechanism to force the EL N+1 installer to ignore 
certain directory trees that are not real partitions (e.g., do not touch 
/usr/local if /usr/local actually is on the same partition as /usr -- 
given that /usr in general must be overwritten to install EL N+1)?

As an aside, when I do this, I keep many things from the EL N 
installation, including many configuration files in /etc so that these 
can be quickly reinstalled.  I personally accomplish this by copying 
these to a subdirectory of a directory for a mount point for a 
filesystem that will not be touched (e.g., /home/prevsys/etc with /home 
on, say, /dev/sda10), using cp -pr to save the required permissions.

These days, I make certain that each physical partition that will be 
reformatted/overwritten by the EL N+1 installer is large enough to 
accommodate the typical growth (bloat?) of the new major release.

Yasha Karant