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doc/start: update hardware recs

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This PR picks up the parts of
https://github.com/ceph/ceph/pull/44466
that were not merged back in January, when that
pull request was raised.

Matters added here:
* improved organzation of matter
* emphasis of IOPs per core over cores per OSD

Signed-off-by: Zac Dover <zac.dover@gmail.com>
This commit is contained in:
Zac Dover 2022-07-15 05:29:11 +10:00
parent 45ecfc6ac7
commit 29c44a3bd6
1 changed files with 23 additions and 14 deletions
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37
doc/start/hardware-recommendations.rst
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@ -21,21 +21,30 @@ data cluster (e.g., OpenStack, CloudStack, etc).
CPU
===
CephFS metadata servers are CPU intensive, so they should have significant
processing power (e.g., quad core or better CPUs) and benefit from higher clock
rate (frequency in GHz). Ceph OSDs run the :term:`RADOS` service, calculate
data placement with :term:`CRUSH`, replicate data, and maintain their own copy of the
cluster map. Therefore, OSD nodes should have a reasonable amount of processing
power. Requirements vary by use-case; a starting point might be one core per
OSD for light / archival usage, and two cores per OSD for heavy workloads such
as RBD volumes attached to VMs. Monitor / manager nodes do not have heavy CPU
demands so a modest processor can be chosen for them. Also consider whether the
host machine will run CPU-intensive processes in addition to Ceph daemons. For
example, if your hosts will run computing VMs (e.g., OpenStack Nova), you will
need to ensure that these other processes leave sufficient processing power for
Ceph daemons. We recommend running additional CPU-intensive processes on
separate hosts to avoid resource contention.
CephFS metadata servers (MDS) are CPU-intensive. CephFS metadata servers (MDS)
should therefore have quad-core (or better) CPUs and high clock rates (GHz). OSD
nodes need enough processing power to run the RADOS service, to calculate data
placement with CRUSH, to replicate data, and to maintain their own copies of the
cluster map.
The requirements of one Ceph cluster are not the same as the requirements of
another, but here are some general guidelines.
In earlier versions of Ceph, we would make hardware recommendations based on
the number of cores per OSD, but this cores-per-OSD metric is no longer as
useful a metric as the number of cycles per IOP and the number of IOPs per OSD.
For example, for NVMe drives, Ceph can easily utilize five or six cores on real
clusters and up to about fourteen cores on single OSDs in isolation. So cores
per OSD are no longer as pressing a concern as they were. When selecting
hardware, select for IOPs per core.
Monitor nodes and manager nodes have no heavy CPU demands and require only
modest processors. If your host machines will run CPU-intensive processes in
addition to Ceph daemons, make sure that you have enough processing power to
run both the CPU-intensive processes and the Ceph daemons. (OpenStack Nova is
one such example of a CPU-intensive process.) We recommend that you run
non-Ceph CPU-intensive processes on separate hosts (that is, on hosts that are
not your monitor and manager nodes) in order to avoid resource contention.
RAM
===