1) How long does it take it Vulnerability scan of 1 linux server including PCI reporting?
2) How many host(Max) scans i can run in parallel with 1 virtual scanner in cloud?
The actual scan time will depend on a variety of factors unique to your environment. I suggest performing a test then report on QID 45038, which is reports the Host Scan Time.
Not sure the exact numbers but you can set these options in your scan Option Profiles.
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