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pv or hvm

CloudxtnyHostCloudxtnyHost Member, Host Rep
edited March 2012 in General

Obviously in this day and age most processors will support either PV or HVM and although PV has the advantage of being a little bit quicker, HVM provides full virtualisation.

What are your guys opinions?

Comments

  • TheHackBoxTheHackBox Member

    I like HVM...

  • CloudxtnyHostCloudxtnyHost Member, Host Rep

    Thehackbox can you expand on why it is your preference ?

  • TheHackBoxTheHackBox Member
    edited March 2012

    Windows support and the ability to run a custom kernel.

  • flyfly Member

    hvm

  • ClintonClinton Member

    PV
    It's much faster and easier to install an OS.

    HVM is nice if you want to run Windows or some odd ISO.

  • quirkyquarkquirkyquark Member

    @Clinton said: It's much faster and easier to install an OS.

    I agree with the easier part, but HVM isn't "much slower" than PV, provided you use the paravirtualized ("PV-on-HVM") drivers. See this slideshow from one of the Xen developers for details -- the bottom line is that PV is about 5% faster for PV-favorable workloads, and much slower than HVM for workloads that favor nested-paging. The memory any VM sees needs to be translated to physical RAM, and nested-paging is a processor feature that performs this address translation in hardware.

    From the slideshow, for example, for PBZIP2 (parallel bzip2), HVM is 12.5% faster than PV; for SPECjbb2005 (server-side java), HVM is 5% slower than PV; for iperf, HVM 32-bit has 45% higher throughput than PV 32-bit, but HVM 64-bit is about 3% slower than PV 64-bit.

  • ClintonClinton Member

    I was talking about a reformat.

    Like installing a PV template vs installing from ISO.

    Those are interesting numbers on PV vs HVM though.

  • flyfly Member

    i need dat archlinux

  • quirkyquarkquirkyquark Member
    edited March 2012

    @Clinton said: I was talking about a reformat.

    Like installing a PV template vs installing from ISO.

    Oh OK, I see :) On that I am with you 100% -- installing/getting HVM to work can be a MONSTER headache.

  • KairusKairus Member

    Any real reason to go with HVM over KVM? What about PV over OpenVZ?

  • quirkyquarkquirkyquark Member

    @Kairus said: What about PV over OpenVZ?

    Not possible with OpenVZ.

  • KairusKairus Member

    @quirkyquark said: Not possible with OpenVZ.

    I mean what's the reasons to go with PV instead of OpenVZ

  • yomeroyomero Member

    I am bored of this threads...

    Thanked by 1Mon5t3r
  • dmmcintyre3dmmcintyre3 Member

    @Kairus said: I mean what's the reasons to go with PV instead of OpenVZ

    Custom kernels (as long as it's modified to support Xen PV), memory management is like a real servers instead of allocation based limits, VPNs work without the host enabling tap/tun/the kernel modules needed for that VPN server, etc. You can run OpenVZ inside Xen PV.

  • Mon5t3rMon5t3r Member

    @yomero said: I am bored of this threads...

    agree.. lets change it to lxc vs other..

  • KairusKairus Member

    @dmmcintyre3 said: Custom kernels (as long as it's modified to support Xen PV), memory management is like a real servers instead of allocation based limits, VPNs work without the host enabling tap/tun/the kernel modules needed for that VPN server, etc.

    Hm, why don't more people offer Xen-PV?

  • CloudxtnyHostCloudxtnyHost Member, Host Rep

    Kairus,

    I believe the normal Xen offering would be Xen-PV.

  • quirkyquarkquirkyquark Member
    edited March 2012

    @httpzoom said: I believe the normal Xen offering would be Xen-PV.

    Yes, from my empirical browsing it's the 2nd most common after OVZ, followed by KVM (catching up fast), Xen-HVM and the remaining laggards (VMWare, etc.)

    @dmmcintyre3 said: Custom kernels (as long as it's modified to support Xen PV),

    I believe the newer linux kernels (2.6.32+) have built-in support, so building a custom kernel shouldn't normally be required. For example, here's part of dmesg from the Ubuntu 3.2.0.-20-virtual kernel:

    [    0.000000] Linux version 3.2.0-20-virtual (buildd@roseapple) (gcc version 4.6.3 (Ubuntu/Linaro 4.6.3)
...
[    0.000000] Booting paravirtualized kernel on Xen
[    0.000000] Xen version: 3.4.4 (preserve-AD)

    And to expand upon the discussion I had with @Clinton earlier in the thread about the ease of installing PV vs. HVM, PV "just works"; the newer kernels also support PV-over-HVM on Xen HVM, but it works best only with Xen 4.0+ -- even that required adding some modules to the initramfs. I couldn't get PV-over-HVM to work on Xen 3.4 -- the disk worked, but the NIC (eth0) wouldn't.

  • MrAndroidMrAndroid Member

    CentOS no longer comes with Xen anymore

  • yomeroyomero Member

    @Mon5t3r said: agree.. lets change it to lxc vs other..

    That could be more interesting...

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