OracleVM Technical FAQ [ID 467664.1]

In this Document
  Purpose
  Questions and Answers
     What happens with the Guest OSes on a host if the host goes down. Will they be started automatically on another host in the same pool?
     Since there is one server pool master and one utility server in a pool, will the pool die if one of these dies? (Single point of failure)
     How is memory allocated in Oracle VM. Is it possible to over allocate like in VMware, or should the total allocated to the guests be less than memory on host?
     Is it possible to take backup of virtual machines while they are running?
     With paravirtualization will all guests be blocked if one guest hangs? (Lack of isolation with paravirtualization)
     Is cloning only possible with the guest shutdown?
     Is there any way to reserve resources to high priority (production) guests in one pool? (Resource management)
     Is it possible to take snapshots while quest is running? Allowing the VM to go back to this point in time?
     Can VM guest have more than one NIC in different mode (bridge & shared)?
     Does VM server (host) support iSCSI and/or utilizing NAS for guest images?
     Can VM guest be configured as PXE boot client?
     What is the difference between 32-bit and 64-bit Oracle VM Server?
     Is Failover Supported?
     Is it possible to use external storage for guest OS'es? What is supported?
     How is memory allocated / shared / coordinated among guest OSes? 
     How is CPU capacity allocated to Virtual Machines?
     Is hard partitioning available?
     Are the actual number of CPUs that are available to the VM visible from within the VM?
     Are the Grid Control agents supported in virtual machines?
     If there are more than one server in a server pool, do they have to be identical?
     If the servers are not identical would Live Migration be possible?

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Applies to:

Oracle Server - Enterprise Edition - Version: 10.2.0.1 and later   [Release: 10.2 and later ]
Oracle VM - Version: 2.1 to 2.2.2   [Release: OVM21 to OVM222]
Linux x86
Linux x86-64
***Checked for relevance on 29-Nov-2010***

Purpose

This document provides quick answers to common questions about Oracle VM from technical perspective.

 

Questions and Answers

What happens with the Guest OSes on a host if the host goes down. Will they be started automatically on another host in the same pool?

If host dies, the status on Oracle VM Manager will be shown as 'Unknown' due to a host die or network temporarily unavailable. Once the host becomes available, then the status of guest will be updated automatically based on guest's real status on a host. Say if the guest is still running or Poweroff, then Running or Powered off status will be showed on Oracle VM Manager respectively. Furthermore, Oracle 2.1.2 version provides the HA feature. When a host with HA enabled dies, guests running on this host can be restarted on other available hosts in the same pool.

Since there is one server pool master and one utility server in a pool, will the pool die if one of these dies? (Single point of failure)

Oracle VM supports multiple utility servers, users can configure multiple servers and provide load-balancing mechanism for choosing which utility server will be used for operations.

For server pool master please see Note 467663.1.

Keep in mind that the actual guest operating systems are never affected by the loss of the manager.  The management application can be restarted and the guests will still be running.  The command line interface can also be used on each physical host in absence of an Oracle VM Manager while it is down.

How is memory allocated in Oracle VM. Is it possible to over allocate like in VMware, or should the total allocated to the guests be less than memory on host?

When a virtual machine is started, agent will compare the free memory available on the host (xend's view) with vm's memory configuration. If there is not enough memory, then vm will not be started. But since a running virtual machine may not use memory as it claims, host's memory may be less than sum of all the running vm's memory.

No overallocation is possible with Oracle VM. You should plan your physical resources accordingly. It is discouraged to overprovision memory for Oracle workloads.

Is it possible to take backup of virtual machines while they are running?

No. But Oracle VM has 'suspend' function, after a virtual machine is suspended, the memory of its running environment is also preserved. It can then continue from where it left after backup.

In addition the guest operating system image can reside on e.g. a NetApp filer where a filer-managed backup can take place.  The guest OS can also run live, network-based backup applications just like a baremetal system would.

With paravirtualization will all guests be blocked if one guest hangs? (Lack of isolation with paravirtualization)

Oracle VM is Xen based and it is definitely not the case with Xen. This will never hang. Paravirtualization does not mean lack of isolation. Oracle VM is exceptionally well isolated.

Is cloning only possible with the guest shutdown?

Yes for current release (Oracle VM Server 2.1).

Again, if you take advantage of certain vendor-specific features in a shared storage environment you may be able to clone additional virtual machines.  Some storage environments offer "copy-on-write" capabilities that allow an image to be cloned from a point in time.  At present none of these management features are driven by the Oracle VM Manager however.

Is there any way to reserve resources to high priority (production) guests in one pool? (Resource management)

Not implement yet in Oracle VM Manager, i.e. all guests are equal for the current release (2.1).  Still not being exposed by Oracle VM Manager  but available directly through the command line +interface on the host.  Please see the documentation for information on the "xm vcpu-set ..." command set.  You can give additional cpu resources to guests with greater service demands.

Is it possible to take snapshots while quest is running? Allowing the VM to go back to this point in time?

Same as before, these features are available on certain vendors' shared storage solutions.

Can VM guest have more than one NIC in different mode (bridge & shared)?

Yes

Does VM server (host) support iSCSI and/or utilizing NAS for guest images?

Yes

Can VM guest be configured as PXE boot client?

Yes but only at the Oracle VM Server. This is not available at the Oracle VM Manager with the current release. (2.1)

What is the difference between 32-bit and 64-bit Oracle VM Server?

There is no difference. On the download site (http://edelivery.oracle.com/oraclevm)choosing x86 32-bit or 64-bit for Platform lists the exact same results with the exact same part numbers. The media that is provided (e.g. V11730-01) is capable to run on both 32-bit and 64-bit hardware with respective support.

Is Failover Supported?

Oracle VM supports failover (for High Availability) starting with 2.1.2 release. This feature is not available in 2.1 or 2.1.1.

Is it possible to use external storage for guest OS'es? What is supported?

Yes. Both SAN (Storage Area Network) and NAS (Network Attached Storage) are supported. There are no direct specifics to consider as long as the configuration is standard and it works. e.g. Qlogic or Emulex cards, Usual SAN storage or iSCSI all is fine as it would be for a bare-metal Linux installation.

How is memory allocated / shared / coordinated among guest OSes? 

Each virtual machine has its own memory size as a guest and when you boot up your system with Oracle VM, all the memory is usable for guests to run in -except a small amount that's allocated for the hypervisor-.

Memory is not overcommitted with Oracle VM so the sum of all guest OS memory sizes must be less than or equal to physical RAM amount. The areas are hard allocated per guest OS.

How is CPU capacity allocated to Virtual Machines?

The default is that all physical CPUs are used to run all the guests.

Is hard partitioning available?

Hard partitioning is available. Please also see related wiki page.

Are the actual number of CPUs that are available to the VM visible from within the VM?

You can define virtual CPUs. Note that one does not know how many physical CPUs there are in a guest. But a guest can have a parameter "vcpus=xx" in vm.cfg, that would show xx number of virtual CPUs. These can also be bound individually against physically cpus in the guest configuration but not from INSIDE the guest.

Are the Grid Control agents supported in virtual machines?

Yes

If there are more than one server in a server pool, do they have to be identical?

In principle, yes.

If the servers are not identical would Live Migration be possible?

If the machines are not identical then live migration may not bepossible. The documentation describes the degree to which the machines must match, but they must at least be the same Manufacturer (AMD/Intel) with the same capabilities.