+++ This bug was initially created as a clone of Bug #1393566 +++

The on-disk metadata used by dm-cache is being updated to allow for performance enhancements.  LVM will need to pass down additional DM table arguments in order to activate these changes.  We need to have a solution ready that is forward/backwards compatible.

--- Additional comment from Zdenek Kabelac on 2017-02-20 05:09:06 EST ---

So lets list the options:

lvm2 new parameter:

1.) --cacheversion   1|2|auto

2.) --cache-metadata-version 2 ?

3.) --metadata-version 2  ?

4.) --cacheformat   1|2|auto    (or maybe this: v1|v2|auto ) ?


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libdm API options:

1.) add new dm_tree_node_set_cache_version(....) 
2.) add new dm_tree_node_set_cache_format(....) 

3.) #define DM_CACHE_FEATURE_FORMAT_2 
4.) #define DM_CACHE_FEATURE_FORMAT_V2 
5.) #define DM_CACHE_FEATURE_VERSION_2 


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ATM I'd prefer the format to be automatically recognized by the 'cache_check' tool - as adding some 'magical' args by lvm2 to the existing configurable set can be problematic for a user - it could be done - but lvm2 will be changing passed option set.

i.e. it's then unclear if we should use:

cache_check  --metadata-version 2

and also

cache_check  --metadata-version 1

or just use it with version 2 ?

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Waiting for more judgment here.