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Date:      Tue, 4 Aug 2020 08:54:41 -0700
From:      Matthew Ahrens <matt@delphix.com>
To:        Steve Wills <swills@freebsd.org>
Cc:        freebsd-fs <freebsd-fs@freebsd.org>, George Wilson <george.wilson@delphix.com>
Subject:   Re: zfs scrub enable by default
Message-ID:  <CAJjvXiEXEdAFXpXkGvt4fymA17kNdp6XkZV5taGKLoP2GvMHbw@mail.gmail.com>
In-Reply-To: <cca34d1a-1892-41ec-ce45-84865100c6e1@FreeBSD.org>
References:  <cca34d1a-1892-41ec-ce45-84865100c6e1@FreeBSD.org>

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This question was raised elsewhere, and I agree with this reply from George
Wilson, my colleague and an expert in the i/o subsystems of ZFS as well as
having lots of experience with customers:

Having scrubs enabled by default is a great idea but at Sun (and Delphix
> too) we found that the impact was often too much for some
> workloads/customers. This is the challenge we faced and why there was never
> a policy to enable it everywhere. We did explore ideas to make the impact
> less and to be able to always scrub. Some of those ideas included periodic
> or continuous scrubs where the impact could be reduced by only scrubbing
> portions of the pool at a time, at a reduced i/o rate. At Delphix, we have
> investigated similar concepts and one of our interns prototyped one of the
> ideas.Much has changed since the early scrub days and revisiting some of
> the earlier ideas and investigating new ones is probably a good topic for
> the community. I do think that just enabling scrub by default without
> further enhancements would still be too impactful for some customers but
> the concept definitely has merit.


--matt

On Mon, Aug 3, 2020 at 9:10 AM Steve Wills <swills@freebsd.org> wrote:

> Hi,
>
> I wonder why we don't enable zfs periodic scrub by default?
>
>
> https://svnweb.freebsd.org/base/head/usr.sbin/periodic/periodic.conf?view=markup#l162
>
> Anyone happen to know?
>
> Thanks,
> Steve
>
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