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From: Neil Brown <neilb@cse.unsw.edu.au>
To: "Bill Rugolsky Jr." <brugolsky@telemetry-investments.com>
Date: Thu, 21 Nov 2002 10:17:21 +1100
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Message-ID: <15836.6145.203067.371300@notabene.cse.unsw.edu.au>
Cc: linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org
Subject: Re: RFC - new raid superblock layout for md driver
In-Reply-To: message from Bill Rugolsky Jr. on Wednesday November 20
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On Wednesday November 20, brugolsky@telemetry-investments.com wrote:
> On Wed, Nov 20, 2002 at 03:09:18PM +1100, Neil Brown wrote:
> >     u32  feature_map     /* bit map of extra features in superblock */
> 
> Perhaps compat/incompat feature flags, like ext[23]?

I thought about that, but am not sure that it makes sense as there is
much less metadata in a raid array than there is in a filesystem.
I think I am happier to have initial code require feature_map == 0 or
it doesn't get loaded, and if it becomes an issue, get user-space to
clear any 'compatible' flags before passing the device to an 'old'
kernel.

> 
> Also, journal information, such as a journal UUID?

As there is no current code, or serious project that I know of, to add
journalling to md (I have thought about it, but it isn't a priority) I
wouldn't like to pre-empt it at all by defining fields now.  I would
rather that presense-of-a-journal be indicated by a bit in the feature map,
and that would imply uuid was stored in one of the current 'pad'
fields.  I think there is plenty of space.

Thanks,
NeilBrown


> 
> Regards,
> 
> 	Bill Rugolsky
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