linux-ext4 - Re: Filesystem freeze vs blockdevice snapshot

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Date:	Mon, 16 Jan 2012 18:03:07 +0100
From:	Asdo <asdo@...ftmail.org>
To:	Amir Goldstein <amir73il@...il.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Filesystem freeze vs blockdevice snapshot

[sorry for double posting : had forgot to remove html]

Thanks but it's still not clear to me.
What do you mean with "clean fs"? is that in any way different from an 
image after a sudden power loss?
Secondarily, how can LVM know what filesystem is underneath and call the 
proper freeze? That's a bare block device, there might not even be a 
filesystem under LVM; or it might be exported via iSCSI to an XYZ 
operating system using the Xyzfs filesystem which Linux knows nothing 
about...
Thank you

On 01/14/12 19:33, Amir Goldstein wrote:
> LVM2 already does the fs freeze for you before taking the snapshot.
> it's the only way to get a block device snapshot of a "clean" fs.
> hope that answers your question.
>
> On Fri, Jan 13, 2012 at 5:30 PM, Asdo <asdo@...ftmail.org 
> <mailto:asdo@...ftmail.org>> wrote:
>
>     Hello all,
>     please excuse the silly question...
>
>     What is the benefit of performing an ext4 fs freeze before taking
>     a snapshot of the underlying block device with LVM2 ?
>
>     Is the freeze step useful or I can go with the snapshot directly?
>
>     And/or is there another use case for the freeze?
>
>     Thank you
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