Re: [PATCH 01/19] btrfs: require at least 4 devices for RAID 6
David Sterba <[email protected]>
| Newsgroups | gmane.linux.kernel.cryptoapi,gmane.linux.kernel,gmane.linux.ports.arm.kernel,gmane.linux.ports.ppc64.devel,gmane.linux.ports.riscv,gmane.comp.file-systems.btrfs,gmane.linux.kernel.cross-arch,gmane.linux.raid |
|---|---|
| Message-ID | <[email protected]> |
On Tue, May 12, 2026 at 07:20:41AM +0200, Christoph Hellwig wrote:
> 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 <[email protected]>
This patch should have been sent separately as it has user visible
impact and can potentially break some setups. 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.