Hi Will,
Yes, adding new pools will increase the number of PG's per OSD. But you can always decrease the number of pg's per OSD by adding new Hosts/OSD's.
When you design a cluster you have to calculate how many pools you're going to use and use that information with PGcalc. (https://ceph.com/pgcalc/)
If you add pools later on they were not part of the original design and you probably will need additional space (OSD's) too.
Kind regards,
Caspar
2018-03-09 11:05 GMT+01:00 Will Zhao <zhao6305@xxxxxxxxx>:
Hi Janne:
Thanks for your response. Approximately 100 PGs per OSD, yes, I
missed out this part.
I am still a little confused. Because 100-PGs-per-OSD rule is the
result of sumation of all used pools .
I konw I can create many pools.Assume that I have 5 pools now , and
the rule has already been met.
So if I create the sixth pool, the total PGs will increased , then
the PGs per OSD will be more then 100.
Will this not violate the rule ?
On Fri, Mar 9, 2018 at 5:40 PM, Janne Johansson <icepic.dz@xxxxxxxxx> wrote:
>
>
> 2018-03-09 10:27 GMT+01:00 Will Zhao <zhao6305@xxxxxxxxx>:
>>
>> Hi all:
>>
>> I have a tiny question. I have read the documents, and it
>> recommend approximately 100 placement groups for normal usage.
>
>
> Per OSD. Approximately 100 PGs per OSD, when all used pools are summed up.
> For things like radosgw, let it use the low defaults (8?) and then expand on
> the pools
> that actually see a lot of data getting into them, leave the rest as is.
>
>
>>
>> Because the pg num can not be decreased, so if in current cluster,
>> the pg num have met this rule, and when I try to create a new pool ,
>> what pg num I should set ? I think no matter what I do , it will
>> violate the pg-num-rule, add burden to osd. This means , if I want my
>> cluster be used by many different users, I should bulid a new cluster
>> for new user ?
>>
>
> No, one cluster can serve a lot of clients. You can have lots of pools if
> you need,
> and those pools can have separate OSD hosts serving them if you need strong
> separation, but still managed from the same cluster.
>
> --
> May the most significant bit of your life be positive.
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