An example, from the "df" output on a system here at Monash:
Filesystem 512-blocks Used Avail Capacity Mounted on
root_domain#root 204800 189466 10624 95% /
usr_domain#usr 614400 433096 153520 74% /usr
var_domain#var 921600 268184 84352 76% /var
var_domain#logs 921600 426274 84352 83% /var/oldlog
s
mail_domain#mail 307200 271694 12384 96% /var/spool/
mail
local_domain#local 921600 508072 379248 57% /usr/local
tmp_domain#tmp 102400 24504 77728 24% /tmp
user_domain#marble 10081440 171782 676208 20% /marble
user_domain#scratch 10081440 1026710 676208 60% /scratch
user_domain#home 10081440 7963790 676208 92% /home
var_domain#ftp 921600 143438 84352 63% /home/ftp
/proc 0 0 0 100% /proc
[...]
Notice that the user_domain is mounted on three separate points, for three
separate functions. Adding a partition to a domain increases its size;
removing one reduces it. The nice thing is that if you add a new hard drive,
add it to a domain, and remove the original partitions from the domain, all
the contents of the domain are moved to the remaining drive, relatively
transparently.
AdvFS is available under Digital Unix; 'twould be very nice to have, IMO.
(I'd do work on it, but I don't have the time, nor the technical knowledge,
to pull it off. :-( ) I can't see it happening before 2.3, though.
Cheers.