Re: [RFC PATCH] btrfs: rescue: Introduce new rescue mount option, rescue=skipdatacsum, to skip data csum verification

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2019/10/29 下午2:53, Roman Mamedov wrote:
> On Tue, 29 Oct 2019 14:21:49 +0800
> Qu Wenruo <wqu@suse.com> wrote:
> 
>> Here we introduce a new rescue= mount option to completely skip data
>> csum check.
>> Since data csum check is completely skipped, for profiles with extra
>> mirrors/copies, it will return the first copy only, which is not
>> optimized, but should be good enough for rescue usage.
>>
>> This option only affects data csum verification, doesn't affect data
>> csum calcuation, so new data write will still be protected by csum (if
>> it doesn't get affected by csum tree corruption).
> 
> Maybe just make the "nodatasum" mount option skip verification of existing
> checksums as well? Actually before seeing this patch I believed "nodatasum"
> already does that.

Nodatasum only applies to new writes, doesn't affect existing csum
verification.

Normally nodatasum is just considered as a performance optimization, not
something we would like to use for rescue usage.

> 
> Also for consistency note that datasum/nodatasum call it just "sum" in the
> mount option name, not "csum".

That makes sense.

Thanks,
Qu


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