zfs discuss - Nov 2008 - ''zeroing out'' unused blocks on a ZFS?

I have RTFM''d through this list and a number of Sun docs at docs.sun 
and can''t find any information on how I might be able to write out
''hard
zeros'' to the unused blocks on a ZFS.  The reason I''d like to
do this is
because if the storage (LUN/s) I''m providing to the ZFS is 
thin-provisioned and doesn''t know about a host O.S. file system and 
whether a previously written disk block still has data on it, only 
knowing it doesn''t if all zero''s are written, then how would I
go about
doing that with ZFS?  I was looking at the command mkfile, which looked 
like it might do it, but I wasn''t sure.  Has anyone done this before
and
can provide the instructions?

On 25 November, 2008 - Dave Brown sent me these 0,8K bytes:
>     I have RTFM''d through this list and a number of Sun docs at
docs.sun
> and can''t find any information on how I might be able to write out
''hard
> zeros'' to the unused blocks on a ZFS.  The reason I''d
like to do this is
> because if the storage (LUN/s) I''m providing to the ZFS is 
> thin-provisioned and doesn''t know about a host O.S. file system
and
> whether a previously written disk block still has data on it, only 
> knowing it doesn''t if all zero''s are written, then how
would I go about
> doing that with ZFS?  I was looking at the command mkfile, which looked 
> like it might do it, but I wasn''t sure.  Has anyone done this
before and
> can provide the instructions?
try turning compression off, then create a huge file (all free space)
with mkfile.. Not sure about the exact bit storage with regards to
checksum etc.. you might want to try with checksum off as well..

/Tomas
-- 
Tomas ?gren, stric at acc.umu.se, http://www.acc.umu.se/~stric/
|- Student at Computing Science, University of Ume?
`- Sysadmin at {cs,acc}.umu.se