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

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doc/rados/operations/stretch-mode.rst: Added Limitations to stretch pool configurations
Reviewed-by: Zac Dover <zac.dover@proton.me>
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Kamoltat (Junior) Sirivadhna 2024-12-09 15:33:28 -05:00 committed by GitHub
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@ -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