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Document the difference between Virtio SCSI and Virtio SCSI single
Also make sure we use the same case in the GuI: VirtIO, and explain why IO Thread requires a specific controller option.
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qm.adoc
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qm.adoc
@ -143,15 +143,19 @@ connected. You can connect up to 6 devices on this controller.
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hardware, and can connect up to 14 storage devices. {pve} emulates by default a
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LSI 53C895A controller.
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+
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A SCSI controller of type _Virtio_ is the recommended setting if you aim for
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A SCSI controller of type _VirtIO SCSI_ is the recommended setting if you aim for
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performance and is automatically selected for newly created Linux VMs since
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{pve} 4.3. Linux distributions have support for this controller since 2012, and
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FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
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containing the drivers during the installation.
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// https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
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If you aim at maximum performance, you can select a SCSI controller of type
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_VirtIO SCSI single_ which will allow you to select the *IO Thread* option.
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When selecting _VirtIO SCSI single_ Qemu will create a new controller for
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each disk, instead of adding all disks to the same controller.
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* The *Virtio* controller, also called virtio-blk to distinguish from
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the Virtio SCSI controller, is an older type of paravirtualized controller
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the VirtIO SCSI controller, is an older type of paravirtualized controller
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which has been superseded in features by the Virtio SCSI Controller.
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[thumbnail="gui-create-vm-hard-disk.png"]
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@ -190,10 +194,12 @@ emulated SCSI controller will relay this information to the storage, which will
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then shrink the disk image accordingly.
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.IO Thread
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The option *IO Thread* can only be enabled when using a disk with the *VirtIO* controller,
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or with the *SCSI* controller, when the emulated controller type is *VirtIO SCSI*.
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With this enabled, Qemu uses one thread per disk, instead of one thread for all,
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so it should increase performance when using multiple disks.
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The option *IO Thread* can only be used when using a disk with the
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*VirtIO* controller, or with the *SCSI* controller, when the emulated controller
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type is *VirtIO SCSI single*.
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With this enabled, Qemu creates one I/O thread per storage controller,
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instead of a single thread for all I/O, so it increases performance when
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multiple disks are used and each disk has its own storage controller.
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Note that backups do not currently work with *IO Thread* enabled.
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