Re: [PATCH v4 13/13] bcache: add stop_when_cache_set_failed to struct cached_dev

[Coly Li <colyli@suse.de>]

On 29/01/2018 8:57 PM, Nix wrote:
> On 27 Jan 2018, Coly Li said:
> 
>> Current bcache failure handling code will stop all attached bcache devices
>> when the cache set is broken or disconnected. This is desired behavior for
>> most of enterprise or cloud use cases, but maybe not for low end
>> configuration. Nix <nix@esperi.org.uk> points out, users may still want to
>> access the bcache device after cache device failed, for example on laptops.
> 
> Actually I'm much interested in the server use case. On laptops, it's
> relatively easy to recover if you know what you're doing, because they
> usually have a user in front of them with console access -- but if a
> remote headless server with a hundred users a thousand miles away has
> its cache device wear out I would really rather the hundred users get
> served, if more slowly, rather than the whole machine going down for
> hours or days until I can get someone there to bash on the hardware!
> 

Hi Nix,

Thanks for the input, I didn't think of such use case before. It makes a
lot sense !

> (Sure, ideally you'd detect the wearing out in advance, but SSDs are not
> always nice and helpful like that and sometimes just go instantly
> readonly or simply vanish off the bus entirely without warning.)
> 

Yes. Then in the v5 patch set, I will add an option for "always"/"auto",
which will leave bcache device alive if the broken cache set is clean.

Thank you all again, for the insight and brilliant suggestion !

Coly Li