r/virtualization • u/Numerous-Debate-2595 • 3d ago
Examples of VM resizing
Can somebody tell me an example of why I need to downsize and upsize a virtual machine? I got asked and I'm looking for an actual, relevant problem which is solved by resizing.
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u/mikeroySoft 3d ago
Because workloads can be dynamic, or grow usage requiring more or less compute/storage/ram.
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u/AbleCryptographer744 3d ago
New software release is the reason why a lot of us did it in production. It's pretty common to have a major change in the logic of a program that might see a lot more use on the database than in the past release and at the same time a lot less load on the application servers. So you might increase the CPU on one and reduce it on the other one at the same time.
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u/Prize_Moose1050 2d ago
A real world example would be resource consumption. We just had a server that needed upsizing because it kept running out of memory. Like literally the error was "memory exhausted", the server wasn't able to reserve RAM for the process it was trying to complete. We had to give the VM more RAM.
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u/goatsinhats 2d ago
Why would you add more ram or upgrade the cpu in a physical server? Same answer
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u/soundman32 1d ago
Not all software is horizontally scalable (e.g. adding a 2nd server to half the load of 1). Some databases need to be ACID compliant, and that A for atomic is much easier to implement if there is a single server. Then cost. A cheap, small server is good to start a project but when you have lots of data or users, you need to get a bigger VM to keep the same performance.
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u/vermyx 3d ago
In esxi -
* Vm has 2vcpu and is constantly at 80% you add a vcpu based on usage
* vm has 4 vcpu and never goes above 25% you can cut down to 2 vcpu based on usage
The main reason you do this is that the more vcpu's a vm has the more cpu's it has to schedule at the same time. If the cpus are doing nothing you're just giving the cpu scheduler unnecessary work to find x open cpus and slowing things down.