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29

That benchmark is only comparing the speed of the native os to a single guest os. Hardly a real world test. I don't think I would put much weight on it. Most of the KVM camp argues that Xen requires too many interrupts and hops between kernel and user space but from most of the more real world benchmarks that I've seen that hasn't really been realized and ...


22

Xen supported virtualization types Xen supports running two different types of guests. Xen guests are often called as domUs (unprivileged domains). Both guest types (PV, HVM) can be used at the same time on a single Xen system. Xen Paravirtualization (PV) Paravirtualization is an efficient and lightweight virtualization ...


20

Xen is an hypervisor that runs on metal (the pc / server) and then hosts virtual machines called domains. A Xen PV domain is a paravirtualized domain, that means the operating system (usually we're talking linux here) has been modified to run under Xen, and there's no need to actually emulate hardware. This should be the most efficient way to go, ...


18

RHEV is the stable version, while oVirt is upstream. Features from oVirt get merged into RHEV when stable and tested. Consider Fedora and RHEL - Fedora is a rich distribution in terms of features and packages, but it's not supported commercially, has a short lifecycle, and is not geared towards stability. RHEL is based on Fedora, but it's code is tested and ...


17

Flashcache, for those who haven't seen it before, is a method for extending the Linux block-cache with a SSD drive. It's cheaper than running a server with a half TB of RAM just for caching. Will this even work? It should. The Linux block-cache works by caching accessed blocks, not files. So long as you're not giving the KVM machines direct access to ...


17

Qemu: QEmu is a complete and standalone software of its own. You use it to emulate machines, it is very flexible and portable. Mainly it works by a special 'recompiler' that transforms binary code written for a given processor into another one (say, to run MIPS code on a PPC mac, or ARM in an x86 PC). To emulate more than just the processor, Qemu ...


16

Having recently gone through the same song and dance with my own management ("VMWare is really expensive! Check out what OSS options there are out there.") I have some observations to share. I/O performance does vary by hypervisor, though CPU performance is much less variant. In general, 'thin' provisioning is a great way to dock I/O performance. Some ...


13

If you defined no CDROM when you created your virtual machine, you can attach the device even to a running domain (virtual machine) by running the following command: virsh attach-disk testbed /dev/sr0 hdc --type cdrom If you already defined a CDROM, but it pointed to an ISO image, in my experience, you can still run the same command. The hdcpart needs to ...


13

First of all, you should avoid using virsh attach-disk with its limited amount of options. Instead, I suggest to specify the exact disk format you prefer in a separate, temporary XML file, like this: <disk type='file' device='disk'> <driver name='qemu' type='qcow2' cache='writeback'/> <source file='/home/gert/kvm/testdomain-vdb.img'/> ...


12

KVM has a much better snapshot capability than what's managed by libvirt; but it depends on qcow2 images. if you use them, just do a savevm <name> on the command console (blocked by libvirt) it won't create a new file, it's a snapshot inside the qcow2 file. test it first, because some KVM versions have it broken.


12

Honestly, I don't see what benefit you would get using any virtualization technology. You are still using one server, there is no reduction in hardware use. As you have only this one server, the possible benefit of being able to migrate virtual machines (maybe even while running) doesn't apply. The amount of work necessary to keep the virt. servers ...


11

virsh dumpxml myvm > foo.xml <edit foo.xml, change the name, move storage> virsh undefine myvm virsh define foo.xml Source: https://www.redhat.com/archives/libvirt-users/2010-October/msg00072.html


10

This is the forwarding delay for interfaces joining the bridge. It's how long it'll be before the interface will be able to do anything. . During this time the bridge will be discovering other bridges and checking that no loops are created. For a better description and the reason for it you need to read up on spanning tree protocol.


10

The latest stable release for libvirt for Ubuntu is version 0.7.5, which doesn't have some newer features (i.e. script hooks and network filters) which make automatic network configuration easier. That said, here's how to enable port forwarding for libvirt 0.7.5 on Ubuntu 10.04 Lucid Lynx. These iptables rules should do the trick: iptables -t nat -I ...


10

There has been a good amount of press regarding the latest AMD processor offering, called Bulldozer. The "Server" version of this part isn't out yet, but the desktop offering is a great view into some of the potential problems of the new stuff. As for the current generation of Server part, all in all the recommendation is fairly good at a generic level. ...


10

The image will not shrink automatically, since when you delete files, you don't actually delete data (this is why undelete works). Qemu has a facility to shrink qcow2 images back, but what the utility does is really deduplicate the zeroes from the disk, leaving all other information intact. So the idea would be to: Zero-fill the drive (dd if=/dev/zero ...


9

You're not done with performance tuning yet. <driver name='qemu' type='raw' cache='writethrough' io='native'/> First is which I/O mechanism to use. QEMU has two asynchronous I/O mechanisms: POSIX AIO emulation using a pool of worker threads and native Linux AIO. Set either io='native' or io='threads' in your XML to benchmark each of these. ...


8

I've got 15 GB of free memory that can be used without having the processes swapped out. No, you don't. total used free shared buffers cached Mem: 32094 31868 225 0 559 16175 You have 225MB of memory free. KiB Swap: 1998844 total, 1113352 used, 885492 free, 16498252 ...


8

You're correct, standard ethernet cables won't work due to the wiring sequence - cisco uses what's called a "rollover cable" for their serial consoles. An example of the pin-out for rollover can be found here: http://pinouts.ru/NetworkCables/rj45_rollover_pinout.shtml It's as simple as pin 8 on one end is swapped to pin 1 on the other end, pin 7 to pin 2, ...


8

In general, I leave HyperThreading ON for VM host servers (VMWare ESXi, KVM, HyperV, etc.). This applies to Intel Nehalem and newer CPUs (5500-series and greater). Additional threads available for scheduling multiple VMs. You may also want to reevaluate the sizing of your guest systems. Typically, it's best to start small on the CPU allocation with virtual ...


8

You are partially correct. Just be careful, as there can be some confusion. KVM is the name of the virtualization technology in the Linux kernel. KVM is also commonly used as the name of a fork (a more accurate name would be qemu-kvm) of the Qemu project with better support for the hardware virtualization. This claim is confirmed by the Qemu project itself. ...


8

Ease of management is achieved by using libvirt which will present the same interface whether you use Xen or KVM. Stability is very much a function of the underlying distribution - Xen only works well with certain (generally older) kernels, whereas KVM is mainline and so gets fixes with every release.


8

When you move the disk image, the installed OS is not aware of that, and it tries to boot with the drivers for the controllers of the previously used virtualization platform. Windows, when it cannot find the driver for the currently installed disk controller, BSOD's and reboots. This is pretty much the same as moving a windows hard drive between different ...


7

You should be using NTFS, unless you have a good reason not, such as a very old legacy application not supporting NTFS. You can have a look at a feature set comparison here, but basically, NTFS has more features (including native file security options that FAT lacks), and there's just no reason to pick FAT over NTFS for an internal disk unless you have to. ...


7

Deleting a file does not actually delete the file, it reduces the number of names pointing to an inode. If both the number of names and the number of open file descriptors to the file reach 0, the data gets deleted. So if you delete a file that's still open by some application, that application can still happily use that file. Only when the last file ...


7

Yes you can install the video hook driver on Vista, but you have to do it manually. To improve speed, right click on the UltraVNC icon on the taskbar and select properties. Then tick the following boxes: Poll Full Screen Poll Foreground Window Poll Window Under Cursor System HookDll If you are using the video hook driver, check if the Video Hook ...


7

We use Xen currently, but I think that in 2011 we will be migrating to KVM. There are some reasons why: KVM development is more integrated with the Linux kernel than Xen's development. KVM vms run as processes to the linux kernel. That has many implications, like scheduling, memory management and etc. That also permits KVM to do overcommit of memory (it's ...


7

Here's an Ubuntu page that shows that you can run in under KVM - https://help.ubuntu.com/community/LXC --additional info-- I've just completed live implementation of LXC under VMware VSphere, as part of it I did a couple of Proof of Concepts that implemented LXC under KVM and VirtualBox as well here's the link: ...


7

Here is a better way to set up port forwarding, using a hook script (source). In /etc/libvirt/hooks/qemu: #!/bin/sh GUEST_NAME= HOST_PORT= GUEST_IPADDR= GUEST_PORT= if [ "$1" = "$GUEST_NAME" ]; then if [ "$2" = start ]; then iptables -t nat -A PREROUTING -p tcp --dport "$HOST_PORT" \ -j DNAT --to "$GUEST_IPADDR:$GUEST_PORT" iptables ...


7

Seems that I finally figured out how to do things I needed. Here is what I did: # kpartx -av /dev/VolGroup00/kvm101_img # vgscan if VolGroup names identical in guest and host systems, then you have to rename guest VolGroup # vgrename <uuid> VolGroupXX uuid of VolGroups you can check in vgdisplay. So, the trick is in activating guest VolGroup: # ...



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