Re: Ongoing Btrfs stability issues

[Goffredo Baroncelli <kreijack@libero.it>]

On 03/10/2018 03:29 PM, Christoph Anton Mitterer wrote:
> On Sat, 2018-03-10 at 14:04 +0200, Nikolay Borisov wrote:
>> So for OLTP workloads you definitely want nodatacow enabled, bear in
>> mind this also disables crc checksumming, but your db engine should
>> already have such functionality implemented in it.
> 
> Unlike repeated claims made here on the list and other places... I
> woudln't now *any* DB system which actually does this per default and
> or in a way that would be comparable to filesystem lvl checksumming.
> 

I agree with you, also nobody warn that without checksum in case of RAID filesystem BTRFS is not capable anymore to check if a stripe is correct or not

> 
> Look back in the archives... when I've asked several times for
> checksumming support *with* nodatacow, I evaluated the existing status
> for the big ones (postgres,mysql,sqlite,bdb)... and all of them had
> this either not enabled per default, not at all, or requiring special
> support for the program using the DB.
> 
> 
> Similar btw: no single VM image type I've evaluated back then had any
> form of checksumming integrated.
> 
> 
> Still, one of the major deficiencies (not in comparison to other fs,
> but in comparison to how it should be) of btrfs unfortunately :-(

COW is needed to properly checksum the data. Otherwise is not possible to ensure the coherency between data and checksum (however I have to point out that BTRFS fails even in this case [*]).
We could rearrange this sentence, saying that: if you want checksum, you need COW...

> 
> 
> Cheers,
> Chris.
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[*] https://www.spinics.net/lists/linux-btrfs/msg69185.html

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