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From: Christoph Hellwig <hch@lst.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: 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>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Dan Williams <dan.j.williams@intel.com>, Chris Mason <clm@fb.com>,
	David Sterba <dsterba@suse.com>, Arnd Bergmann <arnd@arndb.de>,
	Song Liu <song@kernel.org>, Yu Kuai <yukuai@fnnas.com>,
	Li Nan <linan122@huawei.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-raid@vger.kernel.org
Subject: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6
Date: Tue, 12 May 2026 07:20:41 +0200	[thread overview]
Message-ID: <20260512052230.2947683-2-hch@lst.de> (raw)
In-Reply-To: <20260512052230.2947683-1-hch@lst.de>

While the RAID6 algorithm could in theory support 3 devices by just
copying the data disk to the two parity disks, this version is not only
useless because it is a suboptimal version of 3-way mirroring, but also
broken with various crashes and incorrect parity generation in various
architecture-optimized implementations.  Disallow it similar to mdraid
which requires at least 4 devices for RAID 6.

Fixes: 53b381b3abeb ("Btrfs: RAID5 and RAID6")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/btrfs/volumes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a88e68f90564..0b54b97bdad8 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -159,7 +159,7 @@ const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
 		.sub_stripes	= 1,
 		.dev_stripes	= 1,
 		.devs_max	= 0,
-		.devs_min	= 3,
+		.devs_min	= 4,
 		.tolerated_failures = 2,
 		.devs_increment	= 1,
 		.ncopies	= 1,
-- 
2.53.0


WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: 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>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Heiko Carstens <hca@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Alexander Gordeev <agordeev@linux.ibm.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Sven Schnelle <svens@linux.ibm.com>,
	Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Dan Williams <dan.j.williams@intel.com>, Chris Mason <clm@fb.com>,
	David Sterba <dsterba@suse.com>, Arnd Bergmann <arnd@arndb.de>,
	Song Liu <song@kernel.org>, Yu Kuai <yukuai@fnnas.com>,
	Li Nan <linan122@huawei.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, loongarch@lists.linux.dev,
	linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org,
	linux-s390@vger.kernel.org, linux-crypto@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-raid@vger.kernel.org
Subject: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6
Date: Tue, 12 May 2026 07:20:41 +0200	[thread overview]
Message-ID: <20260512052230.2947683-2-hch@lst.de> (raw)
In-Reply-To: <20260512052230.2947683-1-hch@lst.de>

While the RAID6 algorithm could in theory support 3 devices by just
copying the data disk to the two parity disks, this version is not only
useless because it is a suboptimal version of 3-way mirroring, but also
broken with various crashes and incorrect parity generation in various
architecture-optimized implementations.  Disallow it similar to mdraid
which requires at least 4 devices for RAID 6.

Fixes: 53b381b3abeb ("Btrfs: RAID5 and RAID6")
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/btrfs/volumes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index a88e68f90564..0b54b97bdad8 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -159,7 +159,7 @@ const struct btrfs_raid_attr btrfs_raid_array[BTRFS_NR_RAID_TYPES] = {
 		.sub_stripes	= 1,
 		.dev_stripes	= 1,
 		.devs_max	= 0,
-		.devs_min	= 3,
+		.devs_min	= 4,
 		.tolerated_failures = 2,
 		.devs_increment	= 1,
 		.ncopies	= 1,
-- 
2.53.0


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  reply	other threads:[~2026-05-12  5:23 UTC|newest]

Thread overview: 64+ 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 ` Christoph Hellwig
2026-05-12  5:20 ` Christoph Hellwig [this message]
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
2026-05-12 11:42     ` David Sterba
2026-05-13  5:47     ` Christoph Hellwig
2026-05-13  5:47       ` Christoph Hellwig
2026-05-13 20:19       ` David Sterba
2026-05-13 20:19         ` David Sterba
2026-05-14 19:51       ` Goffredo Baroncelli
2026-05-14 19:51         ` Goffredo Baroncelli
2026-05-14 19:57         ` H. Peter Anvin
2026-05-14 19:57           ` H. Peter Anvin
2026-05-15  4:37           ` Christoph Hellwig
2026-05-15  4:37             ` Christoph Hellwig
2026-05-15 14:51           ` David Sterba
2026-05-15 14:51             ` David Sterba
2026-05-15  4:37         ` Christoph Hellwig
2026-05-15  4:37           ` Christoph Hellwig
2026-05-15 16:50           ` Goffredo Baroncelli
2026-05-15 16:50             ` Goffredo Baroncelli
2026-05-15 19:59           ` H. Peter Anvin
2026-05-15 19:59             ` H. Peter Anvin
2026-05-13 16:14   ` H. Peter Anvin
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   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 03/19] raid6: remove __KERNEL__ ifdefs Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 04/19] raid6: move to lib/raid/ Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 05/19] raid6: remove unused defines in pq.h Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 06/19] raid6: remove raid6_get_zero_page Christoph Hellwig
2026-05-12  5:20   ` 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   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 08/19] raid6: improve the public interface Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 09/19] raid6: hide internals Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 10/19] raid6: rework the init helpers Christoph Hellwig
2026-05-12  5:20   ` 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   ` 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   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 13/19] raid6: update top of file comments Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 14/19] raid6_kunit: use KUNIT_CASE_PARAM Christoph Hellwig
2026-05-12  5:20   ` 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   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 16/19] raid6_kunit: cleanup dataptr handling Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 17/19] raid6_kunit: randomize parameters and increase limits Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 18/19] " Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  5:20 ` [PATCH 19/19] raid6_kunit: randomize buffer alignment Christoph Hellwig
2026-05-12  5:20   ` Christoph Hellwig
2026-05-12  9:50 ` cleanup the RAID6 P/Q library v2 Ard Biesheuvel
2026-05-12  9:50   ` Ard Biesheuvel

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