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guest OS boot process faster with less ressources

Posted on 2008-10-23
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We have 4 Windows 2008 64bits guest OS in vmware ESX 3.5 update 2, all VM have been created from the same template.  The physical host has 8 cores and 32GB RAM

Guest OS booting process is slower when the guest has 8GB and faster on the guest with 4GB, no matter how resources are shared (high share or normal share doesn't change anything)  

I even tried to boot the guest OS alone (all other VM down)

Limit setting is set to unlimited.

Is it unusual or normal ?

Thanks




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Question by:quadrumane
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Expert Comment

by:paulsolov
ID: 22790503
This is normal since you're taking more resources from ESX at startup.  During startup the ESX server has to start scheduling the resources and the less it has to schedule the faster your boot up process may be faster at times.
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Author Comment

by:quadrumane
ID: 22791474
Here is what I've been testing.  Only one VM is booting at the time

VM1 - Windows 2008 64bits, 2 cores, 4GB  TIME TO BOOT: 32 seconds

VM2 - Windows 2008 64bits, 2 cores, 8GB  TIME TO BOOT: 39 seconds

VM3 - Windows 2008 64bits, 4cores, 8GB, CPU and memory shares set to high,   TIME TO BOOT: 50s

VM4 - Windows 2008 64bits, 4 cores, 16GB, CPU and memory shares set to high,   TIME TO BOOT: 92s (and 212s when set to 32GB)
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paulsolov earned 2000 total points
ID: 22791553
The more cores you use the slower the system may boot because the scheduler has to pull two or four cores (vCPUs) to sync at the same and process data even though one vCPU may be in use.  This would explain why 4 cores are even slower.  The only time you want to use more than one core (vCPU) is when you have a multithreaded application that can take advantage of it, otherwise the performance may degrade compared to a single vCPU.

I would compare this to a physical environment, one minute boot time is still not too bad.
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by:paulsolov
ID: 22792550
check out this white paper from Dell on Exchange 2007 on VI3 and it gives a good idea on performance for 2 1 vCPU VMs vs 1 2 vCPU VMs and is a fairly accurate guideline
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by:paulsolov
ID: 22792554
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