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doc/rados/operations: improve crush-map-edits.rst

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Signed-off-by: Anthony D'Atri <anthonyeleven@users.noreply.github.com>
(cherry picked from commit 59a894713a)
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Anthony D'Atri 2025-03-14 21:59:57 -04:00 committed by Zac Dover
parent 5ea1c5072e
commit 2c10e50df6
1 changed files with 20 additions and 19 deletions

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doc/rados/operations/crush-map-edits.rst
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@ -227,44 +227,45 @@ and easier to troubleshoot problems when OSDs malfunction (or other hardware
malfunctions) and the administrator needs access to physical hardware.
In the following example, the bucket hierarchy has a leaf bucket named ``osd``
and two node buckets named ``host`` and ``rack``:
In the following example, the CRUSH hierarchy has ``osd`` leaf buckets
and two node-level buckets at the ``host`` level that are in turn children
of a ``rack`` bucket :
.. ditaa::
+-----------+
| {o}rack |
| Bucket |
| {o}rack11 |
+-----+-----+
|
+---------------+---------------+
| |
+-----+-----+ +-----+-----+
| {o}host | | {o}host |
| Bucket | | Bucket |
| {o}host1 | | {o}host2 |
+-----+-----+ +-----+-----+
| |
+-------+-------+ +-------+-------+
| | | |
+-----+-----+ +-----+-----+ +-----+-----+ +-----+-----+
| osd | | osd | | osd | | osd |
| Bucket | | Bucket | | Bucket | | Bucket |
| osd0 | | osd1 | | osd2 | | osd3 |
+-----------+ +-----------+ +-----------+ +-----------+
.. note:: The higher-numbered ``rack`` bucket type aggregates the
lower-numbered ``host`` bucket type.
.. note:: The higher type-number ``rack`` bucket aggregates the
lower type-number ``host`` buckets, which in turn aggregate the basal
type 0 ``osd`` buckets.
Because leaf nodes reflect storage devices that have already been declared
under the ``#devices`` list at the beginning of the CRUSH map, there is no need
to declare them as bucket instances. The second-lowest bucket type in your
hierarchy is typically used to aggregate the devices (that is, the
second-lowest bucket type is usually the computer that contains the storage
media and, such as ``node``, ``computer``, ``server``, ``host``, or
``machine``). In high-density environments, it is common to have multiple hosts
or nodes in a single chassis (for example, in the cases of blades or twins). It
is important to anticipate the potential consequences of chassis failure -- for
example, during the replacement of a chassis in case of a node failure, the
chassis's hosts or nodes (and their associated OSDs) will be in a ``down``
state.
hierarchy is typically used to aggregate the devices: usually
the server that houses the storage drives.
In high-density environments, it is common to have multiple hosts
or nodes in a single chassis: blades or twins. It
is important to anticipate the potential consequences of chassis failure. For
example, during the replacement of a chassis in case of a node failure,
all of the
chassis's hosts and their associated OSDs will be in the ``down``
state and thus unavailable. It is important to avoid placing multiple replicas
or shards of data within a single such chassis, which in this case is
a _failure domain_.
To declare a bucket instance, do the following: specify its type, give it a
unique name (an alphanumeric string), assign it a unique ID expressed as a