What is your ratio between physical and virtual CPU cores?

Cromulent

Cromulent

Cromulent

Soldato
Joined
1 Nov 2007
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England
I'm curious how many virtual machines people put on servers. The most expensive part of most low end servers I'm looking at are the CPU cores so I'm looking to maximise the number of virtual cores on a system but without doing too much harm to the performance of other virtual machines on the server.

Apart from monitoring all the virtual machines to make sure no one is being a "bad neighbour" how many virtual cores do you allocate virtual machines compared with the number of physical cores on the server?

My inital plan was 2 virtual cores for every physical core but I'm curious if this is too conservative?
 
It is.

16 physical cores/32 threads per physical ESXi server, 'bout 100 vCPU's on on each production environment server in normal circumstances. We do see CPU usage warnings from time to time (servers are 5 years old and will be replaced in 2-3 months), but mostly because we use DRS on full auto and migrations do ramp up CPU demand for short time, otherwise VCSA most of the time is reporting healthy without warnings/alerts.
If we are doing maintenance on one datacentre, it's going up to probably 150 vCPU's on single server in second datacentre, and it does go up to 95+% utilization and CPU contention on remaining operational servers, even if I shut down all non-essentials and test&dev servers, but even then slowdown of response is not really noticeable to end users...
 
Yes, it's entire idea behind hypervisor virtualization - you never use entire 100% of VM CPU power at all times, so load is spreading across all VM's across time and temporary spikes in demand just get absorbed cause other VM's not need that power at that same time.

Same with networking, same with ADSL lines - you get loads of bandwidth, but how often you really use all of it and for how long? Provider just gives uplink of 10gbit to they distro device in your neighbourhood and splits that to 30-40 1gbit customers cause they know no one is using it at same time..

In 1990's played with first ADSL fixed lines solutions in my country - we had fixed 1megabit line for 8 128kbit customers devices - usage was never more than half of it.. And it was times where 33k dial-up modems were still just beginning to appear, so not having to use (heftily paid for) phoneline to access Internet AND having it at speed multiple times faster than modem speeds was - we wanted to use our capabilities as much as we could.. ;)
 
Thank you all for the replies. Much appreciated.

I'm planning on having a testing session so hopefully I'll get an idea of what the average is over a period of time.
 
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