Recovering thin provisioned/compressed space

Hello list,

A few days ago I finished migrating a customer from an old v7000 gen1 to a
new v9000. One of the things I proposed was to take advantage of the
compression feature, which works as advertised.
The only caveat found is that the original implementation lacked the
correct ammount of arms x Gb (some documents I found recommend LUNs no
larger than 150Gb) And since you cannot migrate a Load Source drive to a
smaller disk I was forced to do *ENDALC on it for the data to distribute
itself on the remaining drives (I'm talking 800Gb LS vs 146Gb LUNs).

Now, It would seem that STRASPBAL *MOVDTA only moves the data but doesn't
write zeros or otherwise erase the data from the actual disk.
Is there any command to ask the OS or LIC to zero the FREE space on the
drive?
I don't expect IBM i to have space reclamation integrated into the disk
management, but maybe there is or there should be some command to ask for
zeroing of the free space?
Current OS on the machine is 6.1 if it matters.

Thanks in advace for any tips, maybe this ends up being an RFE if it
doesn't exist?

Roberto