> From: zfs-discuss-boun...@opensolaris.org [mailto:zfs-discuss-
> boun...@opensolaris.org] On Behalf Of Jordi Espasa Clofent
> root@sct-caszonesrv-07:~# zfs set compression=on opt/zones/sct-scw02-
> shared

If you use compression=on, or lzjb, then you're using very fast compression.
Should not hurt performance, in fact, may gain performance for highly
compressible data.

If you use compression=gzip (or any gzip level 1 thru 9) then you're using a
fairly expensive compression algorithm.  It will almost certainly hurt
performance, but you may gain more disk space. (Probably not.)

> # copying the previos file to this zone
> ...
> # checking the file size in the origin dir (UFS) and the destination one
> (ZFS with compression enabled)
> ...
> # the both files has exactly the same cksum!

When you enable filesystem compression, it is all done behind the scenes.
It is intended to look and behave exactly the same at the file level, so you
should not see any difference in your files.  Your files should appear to be
exactly the same, and have exactly the same size and checksum as you
otherwise would have expected.  It would be bad if you had to explain to
your users, "Hey you guys, I've enabled filesystem compression, so you
should expect all your files to have different sizes and different
checksums."  The compression & decompression happen at a low level - So all
your applications don't know about it.  

If you want to see the difference in disk usage, I believe "df" and "du"
will report different things...  Or perhaps "ls -l" versus "du" ... 

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