linux-kernel - Re: [PATCH] dm-cache: document zeroing metadata device step

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Date:   Mon, 13 Jul 2020 05:10:45 +0800
From:   Austin Chang <austin880625@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     dm-devel@...hat.com, Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dm-cache: document zeroing metadata device step

On Sun, Jul 12, 2020 at 08:59:32PM +0100, Matthew Wilcox wrote:
> On Mon, Jul 13, 2020 at 03:40:39AM +0800, Austin Chang wrote:
> > +  # When using dmsetup directly instead of volume manager like lvm2,
> > +  # the first 4k of the metadata device should be zeroed to indicate
> > +  # empty metadata.
> > +  dd if=/dev/zero of=/dev/mapper/metadata bs=4k conv=notrunc
> 
> ... don't you need 'count=1' or you'll zero the entire device?

Oops, I copied the command I just used since zeroing the whole metadata
device didn't harm. But 'count=1' should match what I've just written.
I will send a v2 patch later