[ovirt-users] Max amount of datacenters per ovirt engine

[Michal Skrivanek]

> On 26 Apr 2016, at 16:48, Martin Sivak <msivak at redhat.com> wrote:
> 
>> @awels: to add another layer of indirection via a dedicated
>> hosted-engine per outlet seems a little much. we are talking about 500 *
>> 4GB RAM at least in this example, so 2 TB RAM just for management
>> purposes, if you follow engine hardware recommendations?
> 
> I would not go that far. Creating zones per continent (for example)
> might be enough.
> 
>> At least RHEV states in the documentation you support up to 200 hosts
>> per cluster alone.
> 
> The default configuration seems to only allow 250 hosts per datacenter.
> 
> # engine-config -g MaxNumberOfHostsInStoragePool
> MaxNumberOfHostsInStoragePool: 250 version: general

yep, but that liit is there because within a DC there is a lot of assumption for flawless fast enough communication, the most problematic is that all hosts need to access the same storage and the monitoring gets expensive then.
This is a different situation with separate DCs, there’s no cross-DC communication.
I would guess many DCs work great actually.

Too many hosts and VMs in total might be an issue, but since the last official updates there were a lot of changes. E.g. in stable state due to VM status events introduced in 3.6 the traffic required between each host and engine is much lower.
I would not be so afraid of thousands anymore, but of course YMMV

> 
> --
> Martin Sivak
> SLA / oVirt
> 
> On Tue, Apr 26, 2016 at 4:03 PM, Sven Kieske <svenkieske at gmail.com> wrote:
>> On 26.04.2016 14:46, Martin Sivak wrote:
>>> I think that 1000 hosts per engine is a bit over what we recommend
>>> (and support). The fact that all of them are going to be remote might
>>> not be ideal either. The engine assumes the network connection to all
>>> hosts is almost flawless and the necessary routing and distance to
>>> your hosts might not play nice with (for example) the fencing logic.
>> 
>> Hi,
>> 
>> this seems a little surprising.
>> 
>> At least RHEV states in the documentation you support up to 200 hosts
>> per cluster alone.
>> 
>> There are no documented maxima for clusters or datacenters though.
>> 
>> @awels: to add another layer of indirection via a dedicated
>> hosted-engine per outlet seems a little much. we are talking about 500 *
>> 4GB RAM at least in this example, so 2 TB RAM just for management
>> purposes, if you follow engine hardware recommendations?

yeah. currently the added layer of manageiq with HEs everywhere is not that helpful for this particular case. Still, a per-continent split or per-low-latency-area might not be a bad idea.
I can imagine with a bit more tolerant timeouts and refreshes it might work well, with incidents/disconnects being isolated within a DC

>> 
>> But I agree, ovirt does not handle unstable or remote connections that

right. but most of that is again per-DC. You can’t do much cross-DC though (e.g. sharing a template is a pain)

Thanks
michal

>> well, so you might be better of with hundredths of remote engines, but
>> it seems to be a nightmare to manage, even if you automate everything.
>> 
>> My personal experience is, that ovirt does scale at least until about
>> 30-50 DCs managed by a single engine, but that setup was also on a LAN
>> (but I would say it could scale well beyond these numbers, at least on a
>> LAN).
>> 
>> HTH
>> 
>> Sven
>> 
>> 
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