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Our team copied a VM from one Azure subscription onto a new Azure subscription. This VM acts as a Clickhouse client. Both the original and the copied VMs share the same characteristics: Standard B4ms (4 vcpus, 16 GiB memory).

The newly created VM behaves properly, however I noted that it does not perform as well as the original VM. For instance, when trying to run a simple Clickhouse query, this is what both VMs return:

Original VM: Processed 2.45 million rows, 9.79 MB (125.86 million rows/s., 503.44 MB/s.)
New VM:  Processed 2.45 million rows, 9.79 MB (62.26 million rows/s., 249.03 MB/s.)

Do you have any idea what may cause this difference in performance?

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From Microsoft documentation, quoting:

The B-series provides you with the ability to purchase a VM size with baseline performance that can build up credits when it is using less than its baseline. When the VM has accumulated credits, the VM can burst above the baseline using up to 100% of the vCPU when your application requires higher CPU performance

Standard_B4ms has base performance of 90% and max of 400%. Also there are variable of processors that may be used.

Truth could be in credits. Credits should be checked in new and old VM in order to verify if it can burst or not.

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    Thanks for your answer. You may be onto something here! I compared the "CPU Credit Remaining" for each VM over the past month. It turns out that I ran my benchmark test while the new VM's "CPU Credit Remaining" was still ramping up. This could explain the difference in performance between both environments.
    – Sheldon
    Commented Mar 6, 2023 at 2:12

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