FBSD 5.1 and 4.8 sharing the same /home (and /var) possible?

[Stefan A. Deutscher]

Hi  folks,

 I have a 5.1R install working and would like to keep a fall-back 4.8R
on my system as well. From both, I want to be able to use the same
/home, /scratch, and, possibly, /var or at least /var/mail to avoid
duplication of mail. To be nice on my disks, I also ponder sharing swap
space such that the system does not swap to its own system disk (i.e.
5.1R would swap to da0, da2 and da3, 4.8R to da0, da1 and da3) - this
seems to work. The rough disk layout is


   da0 - OS/2
         BSD Swap
   da1 - BSD 5.1R /
         BSD 5.1R swap
         BSD 5.1R /tmp
         BSD 5.1R /var
         BSD 5.1R /usr
   da2 - BSD 4.8R /
         BSD 4.8R swap
         BSD 4.8R /tmp
         BSD 4.8R /var
         BSD 4.8R /scratch
         BSD 4.8R /usr
   da3   BSD 5.1R swap
         BSD 5.1R /home   (63 GB)

Maybe I'll add another 18 or 36 GB disk for /scratch and /backup space.
Now, as per default, the 5.1R install uses ufs2 throughout, the 4.8 one
ufs1. Poking around google I am led to believe that this is not free of
potential for trouble. So, here are my questions, before shooting myself
in the foot

(a)  Is it OK to have the slices to be shared on ufs2, or will 4.8R
     wreck havoc when accessing those (or, better: just not be able to
     see them)

(b)  If ufs2 is not OK for use on both systems, are there any things to
     consider when making them ufs1? I suppose I would have to backup,
     newfs -O1, and restore the /var slice on da1, or is it advisable to
     just make /var/mail a symlink to some separate ufs1 /mail slice?

(c)  Will the background file system checks introduced with 5.x still
     work on these ufs1 slices?


Any thoughts, warings, pointers & hints are most welcome!


  Thanks in advance & cheers,
                                 Stefan


-- 
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Stefan A. Deutscher                             |
Donostia International Physics Center           | office: ++34-943-018174
Universidad del Pais Vasco, Facultad de Quimica | fax   : ++34-943-015600
Departamento de Fisica de Materiales            | home  : ++34-943-270647
Apartado 1072, San Sebastian 20080, Spain       | email : sad at mailaps.org
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