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Date:      Thu, 25 Mar 2021 08:55:12 +0000
From:      Matt Churchyard <matt.churchyard@userve.net>
To:        Mathieu Chouquet-Stringer <me+freebsd@mathieu.digital>
Cc:        "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>
Subject:   RE: Scrub incredibly slow with 13.0-RC3 (as well as RC1 & 2)
Message-ID:  <33eb78e2de404a77b271880dbee4c22e@SERVER.ad.usd-group.com>
In-Reply-To: <YFs3jFT7sEaGeQCe@weirdfishes>
References:  <YFhuxr0qRzchA7x8@weirdfishes> <202103221515.12MFFHRK015188@higson.cam.lispworks.com> <YFi6Lwh3ISn8UMvS@weirdfishes> <YFk11A/j7URClN/l@weirdfishes> <YFm3BTK/J9XY/mCN@weirdfishes> <202103241230.12OCUqur030001@higson.cam.lispworks.com> <YFs3jFT7sEaGeQCe@weirdfishes>

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-----Original Message-----
From: owner-freebsd-fs@freebsd.org <owner-freebsd-fs@freebsd.org> On Behalf=
 Of Mathieu Chouquet-Stringer
Sent: 24 March 2021 12:59
To: Martin Simmons <martin@lispworks.com>
Cc: freebsd-fs@freebsd.org
Subject: Re: Scrub incredibly slow with 13.0-RC3 (as well as RC1 & 2)

On Wed, Mar 24, 2021 at 12:30:52PM +0000, Martin Simmons wrote:
> FWIW, I think the new scrub algorithm was added in 2018.

You're right, git says Wed Nov 15 20:27:01 2017 -0500

> You could try to profile it:
>=20
> https://wiki.freebsd.org/DTrace/Tutorial#Lesson_9._Profile_On-CPU_Kernel_=
Stacks

> dtrace, hello old friend... :-)

> That's the next step...

Just an a aside, I did post a message a few weeks ago with a similar proble=
m on 13 (as well as snapshot issues). Scrub seemed ok for a short while, bu=
t then ground to a halt. It would take 10+ minutes to go 0.01%, with everyt=
hing appearing fairly idle. I finally gave up and stopped it after about 20=
 hours. Moving to 12.2 and rebuilding the pool, the system scrubbed the sam=
e data in an hour, and I've just scrubbed the same system after a month of =
use with about 4 times the data in 3 hours 20. As far as I'm aware, both sh=
ould be using effectively the same "new" scrub code.

Will be interesting if you find a cause as I didn't get any response to wha=
t for me was a complete showstopper for moving to 13.

Matt

--=20
Mathieu Chouquet-Stringer
            The sun itself sees not till heaven clears.
	             -- William Shakespeare --
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