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Re: [Qemu-discuss] Best Intel hardware for qemu


From: Jakob Bohm
Subject: Re: [Qemu-discuss] Best Intel hardware for qemu
Date: Wed, 10 Apr 2019 20:55:02 +0200
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As I wrote, qemu can pass disks (and disk partitions) through without
passing the disk controller through.  To qemu, a physical disk is just
another virtual disk storage format.

But if you want to pass through an entire PCI disk controller (with all
its disks) for faster I/O, then VFIO is needed.

On 10/04/2019 20:40, Lars Bonnesen wrote:
I want to pass local disks to a VM in order to run freenas or similar.

Regards, Lars.

On Wed, Apr 10, 2019, 20:20 Jakob Bohm <address@hidden <mailto:address@hidden>> wrote:

    If you pass through the disk access to your SAN partitions as disk
    accesses to block devices (such as SAN client drivers) in the host
    machine, you don't need VFIO for that.  This can handle nearly
    unlimited number of virtual machines without running out of PCI
    slots in the host machine.  This is the equivalent of "passing
    through a SAN disk" in VMWare, but isn't artificially limited to
    SAN disks (for example, you can layer the Linux multipath drivers
    and/or the Linux disk encryption drivers between the virtual
    machine and the actual SAN).

    If you pass through the network access to your (iSCSI or NBD) SAN
    as network traffic via the general qemu/kvm network features, you
    don't need VFIO for that.  This can handle nearly unlimited number
    of virtual machines without running out of PCI slots in the host
    machine.  This is equivalent to using a "VMWare virtual switch".

    If you dedicate a physical SAN adapter (iSCSI, NBD, SAS or fibre
    channel) to each virtual machine and pass it through to that
    virtual machine, you need VFIO for that.  As on VMWare, this will
    limit you to one virtual machine for each PCI slot in the
    motherboard.

    If you dedicate a physical network adapter (NIC) to each individual
    virtual machine and pass it through to PCI drivers in that virtual
    machine, you need VFIO for that.  This too will limit you to one
    virtual machine for each PCI slot in the motherboard.

    As for passing through raw SCSI devices or busses, I don't know
    if the latest qemu versions have the ability to do this at a
    hardware-independent level like VMWare does (VM sends standard
    SCSI requests to qemu virtual SCSI adapter, qemu sends those
    same SCSI requests to real SCSI hardware via something like the
    Linux "SCSI generic" driver, optionally mapping at most the
    SCSI-level bus address).

    On 10/04/2019 19:42, Lars Bonnesen wrote:
     > But for sure I want passthru - for running virtualized SAN and such
     >
     > Any unofficial list?
     >
     > Regards, Lars.
     >
     > On Wed, Apr 10, 2019, 18:58 Friedrich Oslage
    <address@hidden <mailto:address@hidden>>
     > wrote:
     >
     >> As long as it's VT-x capable and can run Linux, you're good to go.
     >>
     >> It only gets tricky once you start using VFIO (direct passthrough of
     >> host PCI devices to a VM, such as GPUs, NICs or NVMes for
    instance). You
     >> need VT-d support for that and both the CPU and mainboard have to
     >> support it. And not only do they have to support it, they have to
     >> support in a usable way with decent iommu group isolation and
    without
     >> weird bugs. There are no (official) compatibility lists for
    this, it's
     >> still mostly trial and error...
     >>
     >> Regards
     >> Friedrich
     >>
     >> On 4/10/19 2:26 PM, Lars Bonnesen wrote:
     >>> So I am coming from the VMware world (with comprehensive
    compatibillity
     >>> lists) but about to start a project with KVM/Qemu and I would
    like to
     >> setup
     >>> an inexpensive test setup for this purpose.
     >>>
     >>> I am thinking of buying one of SuperMicros IoT-servers like
     >>>
     >>
    https://www.supermicro.com/products/system/Mini-ITX/SYS-E300-9D-4CN8TP.cfm
     >>> Will this be a nice pick for Qemu? Or any VT-supportet system
    will work
     >>> fine?
     >>>
     >>> Regards, Lars.



Enjoy

Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
Transformervej 29, 2860 Søborg, Denmark.  Direct +45 31 13 16 10
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