zpool frag

[John-Mark Gurney]

Allan Jude wrote this message on Sun, Sep 21, 2014 at 11:06 -0400:
> On 2014-09-21 04:57, Beeblebrox wrote:
> > FRAG means fragmentation, right? Zpool fragmentation? That's news to me. If
> > this is real how do I fix it?
> > 
> > NAME      SIZE  ALLOC   FREE   FRAG  EXPANDSZ    CAP  DEDUP  HEALTH  ALTROOT
> > pool1      75.5G  53.7G  21.8G    60%         -    71%  1.00x  ONLINE  -
> > pool2      48.8G  26.2G  22.6G    68%         -    53%  1.00x  ONLINE  -
> > pool3       204G   177G  27.0G    53%         -    86%  1.11x  ONLINE  -
> > 
> > Regards.
> > 
> > 
> > 
> > -----
> > FreeBSD-11-current_amd64_root-on-zfs_RadeonKMS
> > --
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> 
> It is not something you 'fix', it is just a metric to help you
> understand the performance of your pool. The higher the fragmentation,
> the longer it might take to allocate new space, and obviously you will
> have more random seek time while reading from the pool.
> 
> As Steven mentions, there is no defragmentation tool for ZFS. You can
> zfs send/recv or backup/restore the pool if you have a strong enough
> reason to want to get the fragmentation number down.
> 
> It is a fairly natural side effect of a copy-on-write file system.
> 
> Note: the % is not the % fragmented, IIRC, it is the percentage of the
> free blocks that are less that a specific size. I forget what that size is.

Can we get this documented in the zpool man page?  I assume that the
FRAG is the same as:
     fragmentation
                 The amount of fragmentation in the pool.

and that description is woefully lacking..

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."