From: David Sterba <dsterba@suse•cz>
To: "H. Peter Anvin" <hpa@zytor•com>
Cc: kreijack@inwind•it, Goffredo Baroncelli <kreijack@libero•it>,
Christoph Hellwig <hch@lst•de>,
Andrew Morton <akpm@linux-foundation•org>,
Catalin Marinas <catalin.marinas@arm•com>,
Will Deacon <will@kernel•org>, Ard Biesheuvel <ardb@kernel•org>,
Huacai Chen <chenhuacai@kernel•org>,
WANG Xuerui <kernel@xen0n•name>,
Madhavan Srinivasan <maddy@linux•ibm.com>,
Michael Ellerman <mpe@ellerman•id.au>,
Nicholas Piggin <npiggin@gmail•com>,
"Christophe Leroy (CS GROUP)" <chleroy@kernel•org>,
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Palmer Dabbelt <palmer@dabbelt•com>,
Albert Ou <aou@eecs•berkeley.edu>,
Alexandre Ghiti <alex@ghiti•fr>,
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Christian Borntraeger <borntraeger@linux•ibm.com>,
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David Sterba <dsterba@suse•com>, Arnd Bergmann <arnd@arndb•de>,
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Yu Kuai
<yukuai@alb-78bjiv52429oh8qptp•cn-shenzhen.alb.aliyuncs.com>,
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linux-raid@vger•kernel.org
Subject: Re: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6
Date: Fri, 15 May 2026 16:51:58 +0200 [thread overview]
Message-ID: <20260515145158.GP2558453@suse.cz> (raw)
In-Reply-To: <0507CCEF-0548-442F-8703-1D006B5E068B@zytor.com>
On Thu, May 14, 2026 at 12:57:53PM -0700, H. Peter Anvin wrote:
> On May 14, 2026 12:51:59 PM PDT, Goffredo Baroncelli <kreijack@libero•it> wrote:
> >On 13/05/2026 07.47, Christoph Hellwig wrote:
> >> On Tue, May 12, 2026 at 01:42:31PM +0200, David Sterba wrote:
> >
> >>
> >>> The degenerate modes of
> >>> raid0, 5, or 6 are explicit as a possible middle step when converting
> >>> profiles. We can use a fallback implementation for this case if the
> >>> accelerated implementations cannot do it.
> >>
> >> This is not about a degenerated mode. For a degenerated RAID 6, parity
> >> generation uses the RAID 5 XOR routines as the second parity will be
> >> missing. This is about generating two parities for a single data disk,
> >> which must be explicitly selected.
> >>
> >
> >I think that the David concern is : "what happens for an already
> >existing btrfs raid6 3 disks filesystem when the user upgrade the kernel ?"
> >(I am thinking when a new BG needs to be allocated)...
>
> That's what I'm saying – it should invoke the RAID-1 code under the cover (as with 3 disks, D = P = Q.)
Thanks, it was not clear to me what you meant. For the two edge cases
the code should do simple memcpy for both calculations of parity and
recovery.
next prev parent reply other threads:[~2026-05-15 14:52 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-12 5:20 cleanup the RAID6 P/Q library v2 Christoph Hellwig
2026-05-12 5:20 ` [PATCH 01/19] btrfs: require at least 4 devices for RAID 6 Christoph Hellwig
2026-05-12 11:42 ` David Sterba
2026-05-13 5:47 ` Christoph Hellwig
2026-05-13 20:19 ` David Sterba
2026-05-14 19:51 ` Goffredo Baroncelli
2026-05-14 19:57 ` H. Peter Anvin
2026-05-15 4:37 ` Christoph Hellwig
2026-05-15 14:51 ` David Sterba [this message]
2026-05-15 4:37 ` Christoph Hellwig
2026-05-15 16:50 ` Goffredo Baroncelli
2026-05-15 19:59 ` H. Peter Anvin
2026-05-18 5:12 ` Christoph Hellwig
2026-05-20 8:41 ` Qu Wenruo
2026-05-22 0:17 ` Andrew Morton
2026-05-22 0:27 ` Qu Wenruo
2026-05-13 16:14 ` H. Peter Anvin
2026-05-12 5:20 ` [PATCH 02/19] raid6: turn the userspace test harness into a kunit test Christoph Hellwig
2026-05-12 5:20 ` [PATCH 03/19] raid6: remove __KERNEL__ ifdefs Christoph Hellwig
2026-05-12 5:20 ` [PATCH 04/19] raid6: move to lib/raid/ Christoph Hellwig
2026-05-12 5:20 ` [PATCH 05/19] raid6: remove unused defines in pq.h Christoph Hellwig
2026-05-12 5:20 ` [PATCH 06/19] raid6: remove raid6_get_zero_page Christoph Hellwig
2026-05-12 5:20 ` [PATCH 07/19] raid6: use named initializers for struct raid6_calls Christoph Hellwig
2026-05-12 5:20 ` [PATCH 08/19] raid6: improve the public interface Christoph Hellwig
2026-05-12 5:20 ` [PATCH 09/19] raid6: hide internals Christoph Hellwig
2026-05-12 5:20 ` [PATCH 10/19] raid6: rework the init helpers Christoph Hellwig
2026-05-12 5:20 ` [PATCH 11/19] raid6: use static_call for gen_syndrom and xor_syndrom Christoph Hellwig
2026-05-12 5:20 ` [PATCH 12/19] raid6: use static_call for raid6_recov_2data and raid6_recov_datap Christoph Hellwig
2026-05-12 5:20 ` [PATCH 13/19] raid6: update top of file comments Christoph Hellwig
2026-05-12 5:20 ` [PATCH 14/19] raid6_kunit: use KUNIT_CASE_PARAM Christoph Hellwig
2026-05-12 5:20 ` [PATCH 15/19] raid6_kunit: dynamically allocate data buffers using vmalloc Christoph Hellwig
2026-05-12 5:20 ` [PATCH 16/19] raid6_kunit: cleanup dataptr handling Christoph Hellwig
2026-05-12 5:20 ` [PATCH 17/19] raid6_kunit: randomize parameters and increase limits Christoph Hellwig
2026-05-12 5:20 ` [PATCH 18/19] " Christoph Hellwig
2026-05-12 5:20 ` [PATCH 19/19] raid6_kunit: randomize buffer alignment Christoph Hellwig
2026-05-12 9:50 ` cleanup the RAID6 P/Q library v2 Ard Biesheuvel
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