Re: Cache tier READ_FORWARD transition

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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



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