Re: btrfs RAID5 or btrfs on md RAID5?

[DanglingPointer <danglingpointerexception@gmail.com>]

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
>