QEMU KVM Libvirt手册(10): KVM的各种限制

Overcommits

• KVM allows for both memory and disk space overcommit.
• However, hard errors resulting from exceeding available resources will result in guest failures.
• CPU overcommit is also supported but carries performance implications.

Time Synchronization

• kvm-clock 
• NTP or similar network based time keeping protocols are also highly recommended (for VM Host Server and VM Guest) to help maintain a stable time.
• Running NTP inside the guest is not recommended when using the kvm-clock .

MAC addresses

• If no MAC address is specified for a NIC, a default MAC address will be assigned.
• This may result in network problems when more than one NIC receives the same MAC address.
• It is recommended to always assure a unique MAC address has been assigned for each NIC.

Live Migration

• Live Migration is only possible between VM Host Servers with the same CPU features and no physical devices passed from host to guest.
• Guest storage has to be accessible from both VM Host Servers and guest definitions need to be compatible.
• VM Host Server and VM Guests need to have proper timekeeping installed.

User Permissions

• The management tools (Virtual Machine Manager, virsh, vm-install) need to authenticate with libvirt

Suspending/Hibernating the VM Host Server

• Suspending or hibernating the VM Host Server system while guests are running is not supported.

Performance