Subject: Re: FFS journal
To: Bill Studenmund <firstname.lastname@example.org>
From: Thor Lancelot Simon <email@example.com>
Date: 07/03/2006 13:52:28
On Mon, Jul 03, 2006 at 10:16:50AM -0700, Bill Studenmund wrote:
> > * One of the main sources of confusion about journaling is what exactly a
> > journal contains. In the vast majority of journaling filesystems
> > journal only contains modifications made to filesystem metadata
> > (i.e. changes to directories, inodes, inode and block bitmaps). The
> > journal doesn't contain any user data stored in a file.
> You missed the difference between logical and physical journals. You
> really want to do a physical journal as recovery is MUCH simpler.
Solaris journals logical operations, doesn't it? We asked Kirill to
investigate using a compatible on-disk format to the Solaris implementation,
since it is the only mature implementation of journaling for FFS for which
source code is available.
Obviously, he is free to decide to journal physical blocks instead, and
there are good reasons why he might do that. The corresponding project
in FreeBSD is a device driver (actually, part of the GEOM layer) which
journals physical blocks, as I understand it.