Merge pull request ceph#60831 from kamoltat/wip-ksirivad-fix-68338

doc/rados/operations/stretch-mode.rst: Added Limitations to stretch pool configurations
Reviewed-by: Zac Dover <[email protected]>

Author: kamoltat

doc/rados/operations/stretch-mode.rst

@@ -94,6 +94,29 @@ configuration across the entire cluster. Conversely, opt for a ``stretch pool``
 when you need a particular pool to be replicated across ``more than two data centers``,
 providing a more granular level of control and a larger cluster size.
 
+Limitations
+-----------
+
+Individual Stretch Pools do not support I/O operations during a netsplit
+scenario between two or more zones. While the cluster remains accessible for
+basic Ceph commands, I/O usage remains unavailable until the netsplit is
+resolved. This is different from ``stretch mode``, where the tiebreaker monitor
+can isolate one zone of the cluster and continue I/O operations in degraded
+mode during a netsplit. See :ref:`stretch_mode1`
+
+Ceph is designed to tolerate multiple host failures. However, if more than 25% of
+the OSDs in the cluster go down, Ceph may stop marking OSDs as out which will prevent rebalancing
+and some PGs might go inactive. This behavior is controlled by the ``mon_osd_min_in_ratio`` parameter.
+By default, mon_osd_min_in_ratio is set to 0.75, meaning that at least 75% of the OSDs
+in the cluster must remain ``active`` before any additional OSDs can be marked out.
+This setting prevents too many OSDs from being marked out as this might lead to significant
+data movement. The data movement can cause high client I/O impact and long recovery times when
+the OSDs are returned to service. If Ceph stops marking OSDs as out, some PGs may fail to
+rebalance to surviving OSDs, potentially leading to ``inactive`` PGs.
+See https://tracker.ceph.com/issues/68338 for more information.
+
+.. _stretch_mode1:
+
 Stretch Mode
 ============
 Stretch mode is designed to handle deployments in which you cannot guarantee the