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[210.5.38.62]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-b6a76b5d0b4sm8778223a12.29.2025.10.20.18.02.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 20 Oct 2025 18:02:13 -0700 (PDT) Message-ID: <3a3df034-4461-4c35-b170-a5084586d2b3@gmail.com> Date: Tue, 21 Oct 2025 12:02:09 +1100 Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: btrfs RAID5 or btrfs on md RAID5? To: Qu Wenruo , Ulli Horlacher , linux-btrfs References: <20250922070956.GA2624931@tik.uni-stuttgart.de> Content-Language: en-US From: DanglingPointer In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Are there any plans to work on either of the proposed solutions mentioned here to once and for all fix RAID56? On 22/9/25 17:41, Qu Wenruo wrote: > > > 在 2025/9/22 16:39, Ulli Horlacher 写道: >> >> I have 4 x 4 TB SAS SSD (from a deactivated Netapp system) which I >> want to >> recycle in my workstation PC (Ubuntu 24 with kernel 6.14). >> >> Is btrfs RAID5 ready for production usage or shall I use non-RAID >> btrfs on >> top of a md RAID5? > > Neither is perfect. > > Btrfs RAID56 has no journal to protect against write hole. But has the > ability to properly detect and rebuild corrupted data using data > checksum. > > Meanwhile MD raid56 has journal to protect against wirte hole, but has > no checksum to know which data is correct or not. > >> >> What is the current status? >> > > No extra work is done for btrfs RAID56 write hole for a while. > > The experimental raid-stripe-tree has some potential to address the > problem, but that feature doesn't support RAID56 yet. > > > Another solution is something like RAIDZ, which requires block size > > page size support, and extra RAID56 changes (mostly much smaller > stripe length, 4K instead of the current 64K). > > The bs > ps support is not even merged, and submitted patchset lacks > certain features (RAID56 ironically). > And no formal RAIDZ support is even considered. > > So you either run RAID5 for data only and ran full scrub after every > unexpected power loss (slow, and no further writes until scrub is > done, which is further maintanance burden). > Or just don't use RAID5 at all. > > Thanks, > Qu >