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From: "Karl Vogel" <vogelke@pobox.com>
Date: Tue, 2 Jan 2018 15:34:05 -0500
To: freebsd-questions@freebsd.org
Subject: Re: zpool fragmentation
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On Tue, Jan 02, 2018 at 01:52:54PM -0600, Adam Vande More wrote:
> On Tue, Jan 2, 2018 at 12:40 PM, pete wright <nomadlogic@gmail.com> wrote:
>
>> are there any coping mechanisms people use to reduce fragmentation?
> 
> Keep lots of free space.

  If you create an unmounted empty filesystem with a reservation to
  prevent the zpool from filling up, it gives you behavior similar to
  ufs's reserved blocks.  I reserve 5-10% to make sure the system doesn't
  become completely unusable:

    root# zfs create -o reservation=50G -o mountpoint=none rpool/reservation

-- 
Karl Vogel                      I don't speak for the USAF or my company

Sheep learn to recognise celebrity faces from different angles
                                            --"New Scientist", 8 Nov 2017