Hi, I'm wondering when using a cache pool tier if there's an upper bound
on when something written to the cache is flushed back to the backing
pool? Something like a cache_max_flush_age setting? Basically I'm
wondering if I have the unfortunate case of all of the SSD replicas for
a cache pool object all go at once, how far behind is the backing pool
object from the latest data?
Also, am I reading things correctly that if you wanted to turn the
write-back mode into something close to a write-through (though not
exactly), you'd do something like the following?
# ceph osd pool set cachepool cache_target_dirty_ratio 0.00
# ceph osd pool set cachepool cache_min_flush_age 0
That should still ack the client as soon as the replicas were confirmed
on the cachepool layer, but then immediately let the background flusher
start writing the updates to the backing pool, all while still leaving
the object available for further updates from clients, correct? Or does
the background flusher need to lock the object while it writes it to the
backing pool, thus stalling further client updates to to the object
until that completes?
I'm guessing that setting cache_target_dirty_ratio to 0 and
cache_min_flush_age to N, still wouldn't quite implement
cache_max_flush_age since if the object is continually getting updated,
then that timer is continually getting reset, so it never becomes a
candidate to get updated in the backing store, right?
Thanks,
Brian
_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
