On Sun, 4 Dec 2011 16:28:25 -0600 "Leslie Rhorer" [off-list ref] wrote:

I have a system - one that is not expandable - that has relatively limited
RAM, comparatively speaking, and must boot from a usb stick.  The system
hosts a RAID array, but one cannot assume the RAID array is available when
the system boots.  IOW, I want to be able to take down the RAID array for
maintenance, possibly booting the system with no array created, at all.

On the other hand, USB sticks have a limited number of writes available
before they fail, so I don't want the system to be thrashing the flash drive
any more than necessary.  At this time,  I have /var/run, /var/log,
/var/lock, and /tmp mounted as tmpfs file systems.  What I propose is to run
an init script that checks to see if the array is mounted, and if so appends
files in the aforementioned directories to existing directories on the array
and then remounts and binds the directories on the array.  The stop call in
the script will reverse the process so the system can shutdown or so I can
take the array offline after booting for maintenance.  Is this unwise?  Am I
missing something crucial that might cause the system to blow up?

Sounds reasonably sane.

After the bind mount you would need to make sure any process with a file
open in one of those directories re-opens the file.  So you might want to
restart syslogd.

NeilBrown