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Document the difference between Virtio SCSI and Virtio SCSI single

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Also make sure we use the same case in the GuI: VirtIO, and
explain why IO Thread requires a specific controller option.
This commit is contained in:
Emmanuel Kasper 2017-01-04 16:51:27 +01:00 committed by Dietmar Maurer
parent e8503c6cca
commit 81868c7ed9
1 changed files with 12 additions and 6 deletions
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@ -143,15 +143,19 @@ connected. You can connect up to 6 devices on this controller.
hardware, and can connect up to 14 storage devices. {pve} emulates by default a hardware, and can connect up to 14 storage devices. {pve} emulates by default a
LSI 53C895A controller. LSI 53C895A controller.
+ +
A SCSI controller of type _Virtio_ is the recommended setting if you aim for A SCSI controller of type _VirtIO SCSI_ is the recommended setting if you aim for
performance and is automatically selected for newly created Linux VMs since performance and is automatically selected for newly created Linux VMs since
{pve} 4.3. Linux distributions have support for this controller since 2012, and {pve} 4.3. Linux distributions have support for this controller since 2012, and
FreeBSD since 2014. For Windows OSes, you need to provide an extra iso FreeBSD since 2014. For Windows OSes, you need to provide an extra iso
containing the drivers during the installation. containing the drivers during the installation.
// https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation. // https://pve.proxmox.com/wiki/Paravirtualized_Block_Drivers_for_Windows#During_windows_installation.
If you aim at maximum performance, you can select a SCSI controller of type
_VirtIO SCSI single_ which will allow you to select the *IO Thread* option.
When selecting _VirtIO SCSI single_ Qemu will create a new controller for
each disk, instead of adding all disks to the same controller.
* The *Virtio* controller, also called virtio-blk to distinguish from * The *Virtio* controller, also called virtio-blk to distinguish from
the Virtio SCSI controller, is an older type of paravirtualized controller the VirtIO SCSI controller, is an older type of paravirtualized controller
which has been superseded in features by the Virtio SCSI Controller. which has been superseded in features by the Virtio SCSI Controller.
[thumbnail="gui-create-vm-hard-disk.png"] [thumbnail="gui-create-vm-hard-disk.png"]
@ -190,10 +194,12 @@ emulated SCSI controller will relay this information to the storage, which will
then shrink the disk image accordingly. then shrink the disk image accordingly.
.IO Thread .IO Thread
The option *IO Thread* can only be enabled when using a disk with the *VirtIO* controller, The option *IO Thread* can only be used when using a disk with the
or with the *SCSI* controller, when the emulated controller type is *VirtIO SCSI*. *VirtIO* controller, or with the *SCSI* controller, when the emulated controller
With this enabled, Qemu uses one thread per disk, instead of one thread for all, type is *VirtIO SCSI single*.
so it should increase performance when using multiple disks. With this enabled, Qemu creates one I/O thread per storage controller,
instead of a single thread for all I/O, so it increases performance when
multiple disks are used and each disk has its own storage controller.
Note that backups do not currently work with *IO Thread* enabled. Note that backups do not currently work with *IO Thread* enabled.