Re: [PATCH v3 00/13] bcache: device failure handling improvement

On 14 Jan 2018, Coly Li said:

Hi maintainers and folks,

This patch set tries to improve bcache device failure handling, includes
cache device and backing device failures.

The basic idea to handle failed cache device is,
- Unregister cache set
- Detach all backing devices which are attached to this cache set
- Stop all the detached bcache devices
- Stop all flash only volume on the cache set
The above process is named 'cache set retire' by me. The result of cache
set retire is, cache set and bcache devices are all removed, following
I/O requests will get failed immediately to notift upper layer or user
space coce that the cache device is failed or disconnected.

This feels wrong to me. If a cache device is writethrough, the cache is
a pure optimization: having such a device fail should not lead to I/O
failures of any sort, but should only flip the cache device to 'none' so
that writes to the backing store simply don't get cached any more.

Anything else leads to a reliability reduction, since in the end cache
devices *will* fail.

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