[OmniOS-discuss] Fragmentation

[Chris Siebenmann]

>  Is there any way to decrease fragmentation of dr_tank ?
> 
> ------------------------------
> 
> zpool list (Sum of RAW disk capacity without redundancy counted)
> 
> ------------------------------
> 
> NAME      SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
> 
> dr_slow  9.06T  77.6M  9.06T         -     0%     0%  1.00x  ONLINE  -
> dr_tank  48.9T  35.1T  13.9T         -    23%    71%  1.00x  ONLINE  -
> rpool     272G  42.1G   230G         -    10%    15%  1.00x  ONLINE  -

 Note that 'FRAG' probably doesn't mean what you expect it to mean,
and you probably don't need to worry about it.

 The ZFS FRAG percentage here is how fragmented *free space* is, not
how fragmented your data is, and the details are arcane. A pool with
low FRAG has most of its free space in large contiguous segments; a
pool with high FRAG has most of the free space broken up into small
pieces. FRAG is essentially a measure of how hard ZFS will have to
work to find space for new data.

 For more details, you can read:

 https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSZpoolFragmentationMeaning
 https://utcc.utoronto.ca/~cks/space/blog/solaris/ZFSZpoolFragmentationDetails

(These were current as of late 2015, but the details might have changed
slightly since then.)

	- cks