Date: Wed, 27 Jun 2012 10:26:02 -0400 From: John Baldwin <jhb@freebsd.org> To: Pawel Jakub Dawidek <pjd@freebsd.org> Cc: freebsd-hackers <freebsd-hackers@freebsd.org>, "Andrey V. Elsukov" <bu7cher@yandex.ru>, Andriy Gapon <avg@freebsd.org>, freebsd-current <freebsd-current@freebsd.org> Subject: Re: [CFC/CFT] large changes in the loader(8) code Message-ID: <201206271026.02473.jhb@freebsd.org> In-Reply-To: <20120627140817.GC1372@garage.freebsd.pl> References: <4FE9B01C.30306@yandex.ru> <201206270822.25672.jhb@freebsd.org> <20120627140817.GC1372@garage.freebsd.pl>
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On Wednesday, June 27, 2012 10:08:17 am Pawel Jakub Dawidek wrote: > On Wed, Jun 27, 2012 at 08:22:25AM -0400, John Baldwin wrote: > > > I don't think so. Most common case is to configure partitions on top of > > > a mirror. Mirroring partitions is less common. Mostly because of > > > hardware RAIDs being popular. You don't expect hardware RAID vendor to > > > mirror partitions. Partition editors for other OS's won't work, but only > > > because they don't support gmirror. If they wouldn't recognize and > > > support some hardware (or pseudo-hardware) RAIDs there will be the same > > > problem. > > > > Hardware RAIDs hide the metadata from the disk that the BIOS (and disk > > editors) see. Thus, putting a GPT on a hardware RAID volume works fine > > as the logical volume is always seen by all OS's consistently. [...] > > Only if you won't connect this disk to a different controller. Yes, but people do not expect to be able to yank a hardware RAID drive out and hook it up to a "raw" disk controller and have it work. > > [...] The same > > is even true of the "software" RAID that graid supports since the metadata > > is defined by the vendor and thus the logical volume is always seen other > > OS's consistently. > > But is it seen without metadata by the boot loader? Yes. The logical volume shows up as a BIOS disk device. > What I'm trying to say is that it is fair to expect from the user to not > use gmirror-configured disk on different OS. If the user wants to use > this disk in different OS then he has to use format that is recognized > by both. > > Because gmirror is supported by FreeBSD we should improve the support by > teaching boot loader about it. Pretending gmirror is special and > recommending to mirror partitions with it instead of raw disks is not > the solution. > > I really can't see how gmirror is different in this regard from any > other software RAID or volume manager. If you try to use disk that > contains unrecognized metadata the behaviour is undefined (but hopefully > not a panic). It is not gmirror I am complaining about, it is the non-standard use of GPT. Note that gmirror + MBR works fine without violating what little standard there is for the MBR. Using a dedicated GPT partition to hold the gmirrror metadata would work with GPT (but be a good bit harder to work with in terms of GEOM I realize). But as I said, I won't object to these patches. -- John Baldwin
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