Hi Budai,
When you ask "how often the client is retrieving the Cluster Map?" . The obvious answer to that is there is nothing 'often' in it. Whenever there is a change in the map, the monitor will inform the client.
I think you need to read about the CRUSH algorithm in Ceph. Because that will explain you the map changes and data movement. While going through CRUSH, forget there is a monitor node. Just suppose there is a client machine and this client machine READ/WRITE to a cluster ( number of OSDs). Because theoretically a Ceph client can also be a monitor (not at all recommended for practical purposes). Once you have understood CRUSH, I am quite sure that will answer many of your questions.
And feel free to ask about CRUSH. I would be glad to answer.
BR
I think you need to read about the CRUSH algorithm in Ceph. Because that will explain you the map changes and data movement. While going through CRUSH, forget there is a monitor node. Just suppose there is a client machine and this client machine READ/WRITE to a cluster ( number of OSDs). Because theoretically a Ceph client can also be a monitor (not at all recommended for practical purposes). Once you have understood CRUSH, I am quite sure that will answer many of your questions.
And feel free to ask about CRUSH. I would be glad to answer.
BR
On Wed, Jul 15, 2020 at 8:54 AM Budai Laszlo <laszlo.budai@xxxxxxxxx> wrote:
to be more specific: if we have an RBD volume used by a client (a hypervisor, or or mapped with rbd), we assume continuous activity on the volume. How often will the RBD client contact the monitor to get the current map? Are you aware of any documentation page that describes this interaction?
Thank you,
Laszlo
On 7/15/20 8:12 AM, Budai Laszlo wrote:
> Hi Nghia,
>
> in the docs (https://docs.ceph.com/docs/master/architecture/#about-pools) there is the statement "Ceph Clients retrieve a Cluster Map from a Ceph Monitor, and write objects to pools." My question is how often the client is retrieving the Cluster Map? How does the client get the knowledge about a change in the cluster?
>
> Thank you,
> Laszlo
>
> On 7/15/20 7:57 AM, Nghia Viet Tran wrote:
>> Hi Laszlo,
>>
>> Which client are you talking about?
>>
>> On 7/15/20, 11:54, "Budai Laszlo" <laszlo.budai@xxxxxxxxx> wrote:
>>
>> Hello everybody,
>>
>> I'm trying to figure out how often the ceph client is contacting the monitors for updating its own information about the cluster map.
>> Can anyone point me to a document describing this client <-> monitor communication?
>>
>> Thank you,
>> Laszlo
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