This was the question I asked myself when I saw no mention of HYPERVISOR_MEM in file /etc/one/sched.conf. It is the percentage of memory reserved for Hypervisor use.
# HYPERVISOR_MEM: Fraction of total MEMORY reserved for the hypervisor.
# E.g. 0.1 means that only 90% of the total MEMORY will be used
.. will reserve 40% of the total memory for OpenNebula (only 60% RAM will be available for guest VMs). You can choose to over-commit resources by simply specifying a negative value:
is was the preferred method to over-commit resources in OpenNebula.
Well, now things have got even more easier since OpenNebula v4.6. HYPERVISOR_MEM is deprecated now – instead set RESERVED_MEM and RESERVED_CPU attributes to the host via Sunstone -> Infrastructure -> Hosts -> [host]
- RESERVED_CPU in percentage. It will be subtracted from the TOTAL CPU
- RESERVED_MEM in KB. It will be subtracted from the TOTAL MEM
These values can be negative, in that case you’ll be actually increasing the overall capacity so over-commiting host capacity