Re: add volatile flag to PV/LVs (for cache) to avoid degraded state on reboot

Il 2024-01-17 12:08 Zdenek Kabelac ha scritto:
> It's also not completely
> true that even 'writethrough' cache cannot have dirty-blocks (aka -
> only present in cache and origin had failed writes).

Hi, really? From dm-cache docs:

"If writethrough is selected then a write to a cached block will not
complete until it has hit both the origin and cache devices.  Clean
blocks should remain clean."

So I would not expect to see dirty blocks on write-through cache, unless 
the origin device is unable to write at all - which means that removing 
the cache device would be no worse that not having it at all in the 
first place.

What am I missing?

> But ATM we are not seeing it as some major trouble.  Hotspot cache is
> simply not supposed to be randomly removed from your systems - as it
> it's not easy to rebuild.

As a write-through cache should not contain dirty data, using a single 
SSD for caching should be OK. I think that if such expendable (and 
write-through) SSD fails, one should be able to boot without issues.

Thanks.

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Danti Gionatan
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