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

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Message-Id: <200802120908.59602.chris.mason@oracle.com>
Date:	Tue, 12 Feb 2008 09:08:59 -0500
From:	Chris Mason <chris.mason@...cle.com>
To:	Jan Engelhardt <jengelh@...putergmbh.de>
Cc:	David Miller <davem@...emloft.net>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, btrfs-devel@....oracle.com
Subject: Re: BTRFS partition usage...

On Tuesday 12 February 2008, Jan Engelhardt wrote:
> On Feb 12 2008 08:49, Chris Mason wrote:
> >> > 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?
>
> Something looks wrong here. Why would btrfs need to zero at all?
> Superblock at 0, and done. Just like xfs.
> (Yes, I had xfs on sparc before, so it's not like you NEED the
> whitespace at the start of a partition.)

I've had requests to move the super down to 64k to make room for bootloaders, 
which may not matter for sparc, but I don't really plan on different 
locations for different arches.

4k aligned is important given that sector sizes are growing.

-chris
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