[pve-devel] [PATCH docs 3/4] Expand the Precondition section

[Thomas Lamprecht]

On 4/3/19 4:23 PM, Alwin Antreich wrote:
> This patch adds more information about hardware preconditions and
> practices.
> 
> Signed-off-by: Alwin Antreich <a.antreich at proxmox.com>
> ---
>  pveceph.adoc | 57 +++++++++++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 51 insertions(+), 6 deletions(-)
> 
> diff --git a/pveceph.adoc b/pveceph.adoc
> index f5ccdd1..b7378d5 100644
> --- a/pveceph.adoc
> +++ b/pveceph.adoc
> @@ -72,16 +72,56 @@ footnote:[Ceph glossary http://docs.ceph.com/docs/luminous/glossary].
>  Precondition
>  ------------
>  
> -To build a Proxmox Ceph Cluster there should be at least three (preferably)
> -identical servers for the setup.
> -
> -A 10Gb network, exclusively used for Ceph, is recommended. A meshed network
> -setup is also an option if there are no 10Gb switches available, see our wiki
> -article footnote:[Full Mesh Network for Ceph {webwiki-url}Full_Mesh_Network_for_Ceph_Server] .
> +To build a hyper-converged Proxmox + Ceph Cluster there should be at least
> +three (preferably) identical servers for the setup.
>  
>  Check also the recommendations from
>  http://docs.ceph.com/docs/luminous/start/hardware-recommendations/[Ceph's website].
>  
> +.CPU
> +As higher the core frequency the better, this will reduce latency. This will
> +amongst others benefit Ceph's services, as they can process data quicker.  As a
> +simple measure to ease planning dedicate a CPU core (or thread) for each Ceph
> +service to provide enough resources for a stable and enduring Ceph performance.

As talked off list, could you try to break this down to a bit "simpler" sentences,
so that also people with only basics english knowledge can read this more easily?
Would be great, thanks!

> +
> +.Memory
> +Especially in a hyper-converged setup, the memory consumption needs to be
> +carefully monitored. In addition to the intended workload (VM / Container),
> +Ceph needs enough memory to provide good and stable performance. As a rule of
> +thumb, for roughly 1TiB of data, 1 GiB of memory will be used by an OSD. With
> +additionally needed memory for the OSD caching.
> +
> +.Network
> +A 10 Gb or higher bandwidth network, exclusively used for Ceph, is recommended.
> +A meshed network setup is also an option if there are no 10 Gb switches
> +available, see our wiki article footnote:[Full Mesh Network for Ceph
> +{webwiki-url}Full_Mesh_Network_for_Ceph_Server] .
> +
> +To be insistently about networking, as Ceph is a network distributed storage,
> +its traffic needs to be separated onto its own physical network. The volume of
> +traffic especially during recovery will interfere with other services on the
> +same network.
> +
> +Further, estimate your bandwidth needs. While one HDD might not saturate a 1 Gb
> +link, a SSD or a NVMe SSD certainly can. Modern NVMe SSDs will even saturate 10
> +Gb of bandwidth. You also should consider higher bandwidths, as these tend to
> +come with lower latency.
> +
> +.Disks
> +When planning the storage size of your Ceph cluster, it is important to take
> +the recovery time into consideration. Especially with small clusters, the
> +recovery might take a long time. It is advised to use SSDs or NVMe SSDs in
> +small setups to decrease the recovery time and therefore minimise the
> +probability of a subsequent failure event during recovery.
> +
> +In general SSDs or NVMe SSDs will provide more IOPs then spinning disks. This
> +fact and the higher cost may make a xref:pve_ceph_device_classes[class based]
> +separation of pools appealing.  Another possibility to speedup OSDs is to use a
> +faster disk as journal or DB/WAL device. See below on how to create these. If a
> +faster disk is used for multiple OSDs an adequate ratio between OSD and WAL/DB
> +(or journal) device needs to be picked, as otherwise the faster disk will
> +become the bottleneck for all connected OSDs.
> +
>  .Avoid RAID
>  As Ceph handles data object redundancy and multiple parallel writes to disks
>  (OSDs) on its own, using a RAID controller normally doesn’t improve
> @@ -93,6 +133,10 @@ the ones from Ceph.
>  
>  WARNING: Avoid RAID controller, use host bus adapter (HBA) instead.
>  
> +NOTE: Above recommendations should be seen as a rough guidance for choosing
> +hardware. Hence it is still indispensable to test your setup and employ health
> +& performance monitoring.
> +
>  
>  [[pve_ceph_install]]
>  Installation of Ceph Packages
> @@ -316,6 +360,7 @@ operation footnote:[Ceph pool operation
>  http://docs.ceph.com/docs/luminous/rados/operations/pools/]
>  manual.
>  
> +[[pve_ceph_device_classes]]
>  Ceph CRUSH & device classes
>  ---------------------------
>  The foundation of Ceph is its algorithm, **C**ontrolled **R**eplication
>