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Wong Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk, brauner@kernel.org Subject: Re: [RFC PATCH 06/10] ftrfs: add block and inode allocator In-Reply-To: <20260413152101.GX6202@frogsfrogsfrogs> References: <20260413142357.515792-1-aurelien@hackers.camp> <20260413142357.515792-7-aurelien@hackers.camp> <20260413152101.GX6202@frogsfrogsfrogs> Content-Type: text/plain; charset=UTF-8 Date: Tue, 14 Apr 2026 16:11:31 +0200 Message-Id: <1776175891.838384.12723.nullmailer@hackers.camp> Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: On Mon, Apr 13, 2026 at 08:21:01AM -0700, Darrick J. Wong wrote: > No journalling? Or even COW metadata? How is this fault tolerant?? Fair question. The answer is that FTRFS fault tolerance is at the block data layer via Reed-Solomon FEC, not at the metadata consistency layer via journalling or COW. The threat model is radiation-induced single-event upsets (SEU) causing silent bit flips in data at rest on MRAM or NOR flash. Journalling protects against crash consistency (power loss mid-write). COW protects against torn writes. Neither corrects a bit flip that occurred while the device was idle and powered. RS FEC corrects up to 8 symbol errors per 255-byte subblock in place, without requiring a redundant copy. That is the specific gap that FTRFS addresses. The Radiation Event Journal (added in v3) provides a persistent log of every correction event in the superblock, giving operators a map of physical degradation over time. Journalling for crash consistency is a valid concern for v4. The current design assumes the target environment (space, avionics) has well-defined power cycles and controlled shutdown procedures, which reduces the crash consistency risk relative to general-purpose use. This will be documented explicitly in v4. Aurelien DESBRIERES