linux-kernel - Re: BTRFS partition usage...

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Message-Id: <200802120849.34477.chris.mason@oracle.com>
Date:	Tue, 12 Feb 2008 08:49:34 -0500
From:	Chris Mason <chris.mason@...cle.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	btrfs-devel@....oracle.com
Subject: Re: BTRFS partition usage...

On Tuesday 12 February 2008, David Miller wrote:
> From: David Miller <davem@...emloft.net>
> Date: Mon, 11 Feb 2008 23:21:39 -0800 (PST)
>
> > Filesystems like ext2 put their superblock 1 block into the partition
> > in order to avoid overwriting disk labels and other uglies.  UFS does
> > this too, as do several others.  One of the few exceptions I've been
> > able to find is XFS.
> >
> > This is a real issue on sparc where the default sun disk labels
> > created use an initial partition where block zero aliases the disk
> > label.  It took me a few iterations before I figured out why every
> > btrfs make would zero out my disk label :-/
>
> Actually it seems this is only a problem with mkfs.btrfs, it clears
> out the first 64 4K chunks of the disk for whatever reason.

It is a good idea to remove supers from other filesystems.  I also need to add 
zeroing at the end of the device as well.

Looks like I misread the e2fs zeroing code.  It zeros the whole external log 
device, and I assumed it also zero'd out the start of the main FS.

So, if Btrfs starts zeroing at 1k, will that be acceptable for you?

-chris
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