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76 lines
2.6 KiB
ReStructuredText
76 lines
2.6 KiB
ReStructuredText
.. _adjusting-crush:
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=========================
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Adjusting the CRUSH map
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=========================
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There are a few ways to adjust the crush map:
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* online, by issuing commands to the monitor
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* offline, by extracting the current map to a file, modifying it, and then reinjecting a new map
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For offline changes, some can be made directly with ``crushtool``, and
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others require you to decompile the file to text form, manually edit
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it, and then recompile.
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Adding a new device (OSD) to the map
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====================================
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Adding new devices can be done via the monitor. The general form is::
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$ ceph osd crush add <id> <name> <weight> [<loc> [<lo2> ...]]
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where
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* ``id`` is the numeric device id (the OSD id)
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* ``name`` is an alphanumeric name. By convention Ceph uses
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``osd.$id``.
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* ``weight`` is a floating point weight value controlling how much
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data the device will be allocated. A decent convention is to make
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this the number of TB the device will store.
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* ``loc`` is a list of ``what=where`` pairs indicating where in the
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CRUSH hierarchy the device will be stored. By default, the
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hierarchy (the ``what``s) includes ``pool`` (the ``default`` pool
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is normally the root of the hierarchy), ``rack``, and ``host``.
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At least one of these location specifiers has to refer to an
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existing point in the hierarchy, and only the lowest (most
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specific) match counts. Beneath that point, any intervening
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branches will be created as needed. Specifying the complete
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location is always sufficient, and also safe in that existing
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branches (and devices) won't be moved around.
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For example, if the new OSD id is ``123``, we want a weight of ``1.0``
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and the new device is on host ``hostfoo`` and rack ``rackbar``::
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$ ceph osd crush add 123 osd.123 1.0 pool=default rack=rackbar host=hostfoo
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will add it to the hierarchy. The rack ``rackbar`` and host
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``hostfoo`` will be added as needed, as long as the pool ``default``
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exists (as it does in the default Ceph CRUSH map generated during
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cluster creation).
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Note that if I later add another device in the same host but specify a
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different pool or rack::
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$ ceph osd crush add 124 osd.124 1.0 pool=nondefault rack=weirdrack host=hostfoo
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the device will still be placed in host ``hostfoo`` at its current
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location (rack ``rackbar`` and pool ``default``).
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Adjusting the CRUSH weight
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==========================
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You can adjust the CRUSH weight for a device with::
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$ ceph osd crush reweight osd.123 2.0
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Removing a device
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=================
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You can remove a device from the crush map with::
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$ ceph osd crush remove osd.123
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