Re: Cache tier READ_FORWARD transition

["Luis Pabón" <lpabon@redhat.com>]

I think so, but I am not sure what kind of workload would benefit from 
that tune.  Do you have any in mind?  Is the reason for this tuneable 
value to have a more storage efficient caching tier?

- Luis

On 07/07/2014 03:29 PM, Sage Weil wrote:
> On Mon, 7 Jul 2014, Luis Pabon wrote:
>> Hi all,
>>      I am working on OSDMonitor.cc:5325 and wanted to confirm the following
>> read_forward cache tier transition:
>>
>>      readforward -> forward || writeback || (any && num_objects_dirty == 0)
>>      forward -> writeback || readforward || (any && num_objects_dirty == 0)
>>      writeback -> readforward || forward
>>
>> Is this the correct cache tier state transition?
> That looks right to me.
>
> By the way, I had a thought after we spoke that we probably want something
> that is somewhere inbetween the current writeback behavior (promote on
> first read) and the read_forward behavior (never promote on read).  I
> suspect a good all-around policy is something like promote on second read?
> This should probably be rolled into the writeback mode as a tunable...
>
> sage
>
>