contain holes – can't swap on it.
root@home# mkfile 512m /var/swapfile
root@home# swap -a /var/swapfile
“/var/swapfile” may contain holes – can’t swap on it.
the above is ok for UFS, but not work in ZFS.
Solution:
root@home# zfs create -V 1gb rpool/swapfile
root@home# swap -a /dev/zvol/dsk/rpool/swapfile
Good articles on Swap
http://blogs.sun.com/jimlaurent/entry/solaris_faq_myths_and_facts