fcontext nightmare - Help please?

[Edward Harvey]

I'm managing an amazon virtual machine, with 8G / partition, and a larger
secondary storage device attached.  I enabled selinux, and I'm trying to
make things work (and keep things secure) while migrating some things such
as the ldap & mysql directories to the second device.
 
As far as I know, simply extending the / partition isn't an option (not LVM)
...  Conceivably I could just make a clone larger machine, but there are a
lot of advantages to having the separate storage device... which can be LVM,
and prevents the / filesystem from getting filled up, and can be
detached/reattached to other machines, etc etc.  So I'm trying like heck to
keep the second storage device separate.
 
Here's the problem:
 
I mount /data, and now I've got to move & preserve things like the
/var/lib/mysql directory to a subdir of /data, while preserving selinux
types and everything.  I started out by simply mimicking the / structure ...
                sudo mount /data
                sudo mkdir -p /data/var/lib
                sudo chown --reference=/ /data
                sudo chcon --reference=/ /data
                sudo chmod --reference=/ /data
                sudo chown --reference=/var /data/var
                sudo chcon --reference=/var /data/var
                sudo chmod --reference=/var /data/var
                sudo chown --reference=/var/lib /data/var/lib
                sudo chcon --reference=/var/lib /data/var/lib
                sudo chmod --reference=/var/lib /data/var/lib
                And finally
                cd /var/lib ; sudo tar cpf - --selinux mysql | (cd
/data/var/lib ; sudo tar xpf - --selinux) ; cd -
 
I understand that chcon is not persistent...
And after all the above was done, I meticulously examined all the contexts
of all those directories and confirmed they do match the original...
 
Unfortunately, as soon as I start mysqld, the context of /data/var/lib/mysql
gets reset.  I don't know how or why that is happening, but I presume it's
because I haven't set the fcontext.  So ...
 
I want to write a script that walks through the whole /var/lib/mysql
directory, and creates matching fcontexts for /data/var/lib/mysql.  Better
yet ... I would like to create fcontext applied to /data which is a complete
replica of /
 
Here is where I'm getting stuck.  I can do "semanage fcontext -l" and I see
all the information, but it's not in a format that's suitable to modify and
feed back into semanage.  I can do "semanage -o -" but it only says
"fcontext -D" which is not helpful.
 
I can't seem to find any combination of commands that will allow me to get
all the fcontexts of / (or a relatively large subdir of /) and modify them
with the /data prefix to feed back into semanage.
 
Help please?
 
Thanks...