Hi,
On 8/18/19 12:06 AM, EDH - Manuel Rios Fernandez wrote:
Hi ,
Whats the reason for not allow balancer PG if objects are
inactive/misplaced at least in nautilus 14.2.2 ?
https://github.com/ceph/ceph/blob/master/src/pybind/mgr/balancer/module.py#L874
*snipsnap*
We can understood that balancer cant work with unknow pgs states and
inactive states. But… missing and misplaced…
The degraded state indicates that some data is missing within the pg, or
one replicate is not up to date. See below for an example.
Hope some developer can clarify that. This lines cause a lot of
problem at least in nautilus 14.2.2
Case example:
* Pool Size 1, upgraded to Size 2. Cluster become Warning with
misplaced and degraded. Some objects are don’t recovery from
degraded state due “OSD backfullfill_toofull “due OSDs became full
instead of even distributed and balanced, because balancer code
exclude it.
Updating to size 2 requires all PGs to have two replicates. After
changing the size settings, the PGs will be undersized+degraded, since
only one instance exists (->undersized). The second replicate will be
created during the backfilling, and after the complete content of the PG
the state will change to active+clean.
Degraded state can also happen during restart of an OSD. If write are
not blocked during the restart (e.g. there are enough replicates
active), the other instances of a PG will have updated data. This data
needs to be replicated to the restarted OSD after it is available again.
A similar situation happens during balancing or moving PG in general; if
a PG is not transfered completely yet, new writes may be send to either
the old set of OSDs (and need to be backfilling afterwards), or send to
the new set (and are considered degraded, since from the a point-in-time
view of the cluster they are not present on the acting set of OSDs). I'm
not 100% sure which way is implemented in Ceph, gut feelings point to
the later one.
Degraded thus refers to a state where a PG does not fulfill its
replication requirements and should thus be handled as an error or
warning state. And you do not want the balancer to interfere with this
state.
Regards,
Burkhard
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