Hi All, Time for a little Saturday evening Ceph related quiz.
>From this documentation page http://ceph.com/docs/master/rados/operations/cache-tiering/ It seems to indicate that you can either flush/evict using relative sizing (cache_target_dirty_ratio) or absolute sizing (target_max_bytes). But the two are separate methods and are mutually exclusive. Ie flush at 80% or when you hit the number of bytes specified The same goes for the max_age parameters, ie it will flush all objects older than 300 seconds no matter how full the pool is. However this documentation page https://ceph.com/docs/master/dev/cache-pool/ Seems to indicate that the target_max_bytes is actually the number of bytes that the cache_target_dirty_ratio uses to calculate the size of the cache pool it has to work with. And that the max_age parameters just make sure objects aren't evicted too quickly. 1. Maybe, I'm reading it wrong but they appear conflicting to me, Which is correct? The following questions may be invalid depending on the answer to #1 2. Assuming link #1 is correct, is it possible to have multiple cache pools on group of SSD's and how does Ceph work out capacity for each pool? 3. Assuming #2 is correct, I can also specify min_age variables without overriding the target_max_bytes and cache_target_dirty_ratio? So assuming link #2 is correct (which makes more sense to me), if I had the following configuration target_max_bytes = 10,000,000,000 cache_target_dirty_ratio = .4 cache_full_dirty_ratio = .8 cache_min_flush_age = 60 cache_min_evict_age = 120 Then are the following assumptions true:- 1. I have a cache pool that is 10G total in size, regardless of the actual size of the pool 2. When the pool has 4G of dirty bytes in it, it will start trying to flush them as long as they are older than 60 seconds 3. When the pool is 8G full it will start evicting all objects that are older than 120 seconds in a LRU order 4. If I manage to fill the pool up to 10G, Ceph will block until free space becomes available from evictions 5. If I had a 100G worth of SSD capacity after replication, I could have 10 of these cache pools (disregard performance concerns) Many Thanks for any answers, Nick _______________________________________________ ceph-users mailing list ceph-users@lists.ceph.com http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
