Following are what i did after replace HD. i found what you mean the 4a here.
1.During boot, press ctrl +c
Press CTRL-C for special boot menu
(1) Normal boot.
(2) Boot without /etc/rc.
(3) Change password.
(4) Initialize owned disks (4 disks are owned by this filer).
(4a) Same as option 4, but create a flexible root volume.
(5) Maintenance mode boot.
Selection (1-5)?
2. Then select 4, initialize disks.
3. After system normal start, run command "setup", then do a setup follow the prompt.
nas> setup
The setup command will rewrite the /etc/rc, /etc/exports,
/etc/hosts, /etc/hosts.equiv, /etc/dgateways, /etc/nsswitch.conf,
and /etc/resolv.conf files, saving the original contents of
these files in .bak files (e.g. /etc/exports.bak).
Are you sure you want to continue? [yes]