Enabling compression on ZFS - a practical example

cp after enabling

After enabling compression:

[dan@zuul:~] $ zpool list
NAME     SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
system   452G   365G  87.5G         -    52%    80%  1.00x  ONLINE  -


I had this large file:

-rw-r-----  1 rsyncer  rsyncer  68630478685 Apr  3 09:12 bacula.dump


I copied it:

[rsyncer@zuul ~/backups/Bacula]$ cp bacula.dump bacula.dump.compressed


I checked space:

[dan@zuul:~] $ zpool list
NAME     SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
system   452G   372G  79.5G         -    54%    82%  1.00x  ONLINE  -


That's a 63GB file copied, and using only 8G or so.

Now lets move it back:

[rsyncer@zuul ~/backups/Bacula]$ mv bacula.dump.compressed bacula.dump

A short while later:

[dan@zuul:~] $ zpool list
NAME     SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
system   452G   306G   146G         -    46%    67%  1.00x  ONLINE  -


Wow! Another 66G of free space. We went from 82% full to 67% full.

Moral: Always turn compression on.