Hi Burkhard,
On 29/09/16 15:08, Burkhard Linke wrote:
AFAIK evicting an object also flushes it to the backing storage, so
evicting a live object should be ok. It will be promoted again at the
next access (or whatever triggers promotion in the caching mechanism).
For the dead 0-byte files: Should I open a bug report?
Not sure whether this is a bug at all. The objects should be evicted and
removed if the cache pool hits the max object thresholds.
d'oh, Ceph and it's hidden gems ;) That was it. Yes, we have currently
no hard object limit (target_max_objects) as we have target_max_bytes
set and thought that would be enough. After setting target_max_objects
(even to a ridiculous high number, I used 200 millions, so double the
amount we have) and Ceph immediately started dropping objects (and
blocking all client IO :( )
Is this behavior documented somewhere? From the cache tiering doc it
looked like you either set target_max_bytes OR target_max_objects and
not both (although I always wondered what sense does it make to talk
about objects on a cache layer, as it's nature is that it is space bound
and it is less than the backing pool. I even wondered why
target_max_bytes is even necessary, as Ceph knows how much space is
available. I mean optionally restricting it further is ok, in case you
want to have two Cache pools on the same set of fast disks / SSds, but
IMHO it could be optionally and in case of just one pool use whats there)
Anyway, thanks a lot for the help. We will see how we can get some
downtime in order to set a limit and cleanup the backlog of stale
objects from the cache.
Greetings
-Sascha-
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