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30

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 ...


27

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 ...


26

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 ...


25

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, ...


22

stop the VM run qemu-img resize vmdisk.img +10G to increase image size by 10Gb start the VM, resize the partitions and LVM structure within it normally


19

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 ...


18

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 ...


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 ...


15

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 ...


15

I'd like to start with a note that you should avoid using virsh attach-disk with its limited amount of options. Instead, I'd suggest to specify the exact disk format you prefer in a separate, temporary XML file or by using the virt-manager GUI application (for the latter, skip the first step). Create a temporary file with a disk definition like this one ...


13

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 ...


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

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


12

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 ...


12

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 was confirmed by the QEMU project, but ...


11

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.


11

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

When working together, KVM arbitrates access to the CPU and memory, and QEMU emulates the hardware resources (hard disk, video, USB, etc.). When working alone, QEMU emulates both CPU and hardware.


11

TRIM works at the filesystem level so as you're giving your KVM domains a raw block device then you need to enable TRIM from within the domain; your host can't know the domains filesystem utilisation without examining it. To enable this you need to ensure there's a discard='unmap' attribute added to the disk definition in the XML for the domain, this is ...


10

Edit /etc/network/interface and remove all but one of the gateway statements.


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

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. ...


9

Yo dawg. Yes, you can, although it's a lot slower.


9

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 ...


8

rsync --ignore-existing --sparse ... To create new files in sparse mode Followed by rsync --inplace ... To update all existing files (including the previously created sparse ones) inplace.


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

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 ...


8

Best practice: Don't run anything but the hypervisor on the host.


8

I'll ask, how important is it that you specifically use KVM? My preference for the type of solution you're inquiring about is to build around VMWare ESXi. You can build an all-in-one server running VMWare ESXi booting from flash media (SDHC, USB, CF) and leverage the DirectPath I/O (PCI-passthrough) available on current servers to present a SAS/SATA HBA to ...


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, ...



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