Greetings,I am using bcache in conjunction with SnapRAID, which works on the FS-level, and I have noticed that parity syncs as well as scrubs read data from the cache rather than the backing device. This probably not a problem when creating parity for new files, but could be a problem when running scrubs, as the parity is never checked against data on disk since bcache hides it.
I would therefore very much like a cache_mode that would bypass any and all reads, that can be enabled for the duration of a SnapRAID sync or scrub. For writes I suppose this mode should act the same as "none".
This opportunity could be taken to verify data on cache as well; read from both backing and cache and invalidate the cache page if it differs from the backing data, while satisfying the actual read from backing in any case.
Perhaps something like this is already possible and I'm just not seeing it?I know I can detach backing devices, but to my understanding that also invalidates all its cached pages and I would obviously like to keep them for this purpose.
Looking forward to your opinions, Best regards, Andy
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