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Chapter 6. Override Ceph behavior
As a storage administrator, you need to understand how to use overrides for the Red Hat Ceph Storage cluster to change Ceph options during runtime.
6.1. Setting and unsetting Ceph override options
You can set and unset Ceph options to override Ceph’s default behavior.
Prerequisites
- A running Red Hat Ceph Storage cluster.
- Root-level access to the node.
Procedure
To override Ceph’s default behavior, use the
ceph osd setcommand and the behavior you wish to override:Syntax
ceph osd set FLAGOnce you set the behavior,
ceph healthwill reflect the override(s) that you have set for the cluster.Example
[ceph: root@host01 /]# ceph osd set noout
To cease overriding Ceph’s default behavior, use the
ceph osd unsetcommand and the override you wish to cease.Syntax
ceph osd unset FLAGExample
[ceph: root@host01 /]# ceph osd unset noout
| Flag | Description |
|---|---|
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|
Prevents OSDs from being treated as |
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Prevents OSDs from being treated as |
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Prevents OSDs from being treated as |
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Prevents OSDs from being treated as |
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Makes a cluster appear to have reached its |
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Ceph will stop processing read and write operations, but will not affect OSD |
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| Ceph will prevent new backfill operations. |
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| Ceph will prevent new rebalancing operations. |
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| Ceph will prevent new recovery operations. |
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| Ceph will prevent new scrubbing operations. |
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| Ceph will prevent new deep scrubbing operations. |
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| Ceph will disable the process that is looking for cold/dirty objects to flush and evict. |
6.2. Ceph override use cases
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noin: Commonly used withnooutto address flapping OSDs. -
noout: If themon osd report timeoutis exceeded and an OSD has not reported to the monitor, the OSD will get markedout. If this happens erroneously, you can setnooutto prevent the OSD(s) from getting markedoutwhile you troubleshoot the issue. -
noup: Commonly used withnodownto address flapping OSDs. -
nodown: Networking issues may interrupt Ceph 'heartbeat' processes, and an OSD may beupbut still get marked down. You can setnodownto prevent OSDs from getting marked down while troubleshooting the issue. full: If a cluster is reaching itsfull_ratio, you can pre-emptively set the cluster tofulland expand capacity.NoteSetting the cluster to
fullwill prevent write operations.-
pause: If you need to troubleshoot a running Ceph cluster without clients reading and writing data, you can set the cluster topauseto prevent client operations. -
nobackfill: If you need to take an OSD or nodedowntemporarily, for example, upgrading daemons, you can setnobackfillso that Ceph will not backfill while the OSDs isdown. -
norecover: If you need to replace an OSD disk and don’t want the PGs to recover to another OSD while you are hotswapping disks, you can setnorecoverto prevent the other OSDs from copying a new set of PGs to other OSDs. -
noscrubandnodeep-scrubb: If you want to prevent scrubbing for example, to reduce overhead during high loads, recovery, backfilling, and rebalancing you can setnoscruband/ornodeep-scrubto prevent the cluster from scrubbing OSDs. -
notieragent: If you want to stop the tier agent process from finding cold objects to flush to the backing storage tier, you may setnotieragent.
