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Date:      Mon, 28 Aug 2023 10:23:09 -0400
From:      Alexander Motin <mav@FreeBSD.org>
To:        Pete Wright <pete@nomadlogic.org>, freebsd-current@freebsd.org
Subject:   Re: zfs autotrim default to off now
Message-ID:  <de2b9081-4f3b-c19b-b658-08dd9acb563d@FreeBSD.org>
In-Reply-To: <cpzqsgncysqm4xwarzue2n6vxpzw2yl4owlcwf64mcgzleclbb@eltdofcwp6iw>
References:  <cpzqsgncysqm4xwarzue2n6vxpzw2yl4owlcwf64mcgzleclbb@eltdofcwp6iw>

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Hi Pete,

On 27.08.2023 23:34, Pete Wright wrote:
> looking at a recent pull of CURRENT i'm noticing this in the git logs:
> 
> #15079 set autotrim default to 'off' everywhere
> 
> which references this openzfs PR:
> https://github.com/openzfs/zfs/pull/15079
> 
> 
> looking at the PR i'm not seeing a reference to a bug report or anything, is
> anyone able to point me to a bug report for this.  it seems like a pretty major
> issue:
> "As it turns out having autotrim default to 'on' on FreeBSD never really worked
> due to mess with defines where userland and kernel module were getting different
> default values (userland was defaulting to 'off', module was thinking it's
> 'on')."
> 
> i'd just like to make sure i better understand the issue and can see if my
> systems are impacted.

You are probably misinterpreting the quote.  There is nothing wrong with 
the autotrim itself, assuming your specific devices properly handle it. 
It is just saying that setting it to "on" by default on FreeBSD, that 
was done to keep pre-OpenZFS behavior, appeared broken for a while.  So 
that commit merely confirmed the status quo.  It should not affect any 
already existing pools.  On a new pool creation the default is now 
officially "off", matching OpenZFS on other platforms, but there is no 
reason why you can not set it to "on", if it is beneficial for your 
devices and workloads.  As alternative, for example, you may run trim 
manually from time to time during any low activity periods.

-- 
Alexander Motin



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