From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: RFC - new raid superblock layout for md driver Date: Thu, 21 Nov 2002 10:17:21 +1100 Sender: linux-kernel-owner@vger.kernel.org Message-ID: <15836.6145.203067.371300@notabene.cse.unsw.edu.au> References: <15835.2798.613940.614361@notabene.cse.unsw.edu.au> <20021120085838.A9206@ti19> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: message from Bill Rugolsky Jr. on Wednesday November 20 To: "Bill Rugolsky Jr." Cc: linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org List-Id: linux-raid.ids 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