Red Hat Summit Red Hat SummitSupportConsoleDéveloppeursCommencer un essaiContact

13.5. Optimizing virtual machine I/O performance

The input and output (I/O) capabilities of a virtual machine (VM) can significantly limit the VM’s overall efficiency. To address this, you can optimize a VM’s I/O by configuring block I/O parameters.

13.5.1. Tuning block I/O in virtual machines
Copier lien

When multiple block devices are being used by one or more VMs, it might be important to adjust the I/O priority of specific virtual devices by modifying their I/O weights.

Increasing the I/O weight of a device increases its priority for I/O bandwidth, and therefore provides it with more host resources. Similarly, reducing a device’s weight makes it consume less host resources.

Note

Each device’s weight value must be within the 100 to 1000 range. Alternatively, the value can be 0, which removes that device from per-device listings.

Procédure

To display and set a VM’s block I/O parameters:

  1. Display the current <blkio> parameters for a VM:

    # virsh dumpxml VM-name 

    <domain>
  [...]
  <blkiotune>
    <weight>800</weight>
    <device>
      <path>/dev/sda</path>
      <weight>1000</weight>
    </device>
    <device>
      <path>/dev/sdb</path>
      <weight>500</weight>
    </device>
  </blkiotune>
  [...]
</domain>
    Copy to Clipboard Toggle word wrap

  2. Edit the I/O weight of a specified device: 

    # virsh blkiotune VM-name --device-weights device, I/O-weight
    Copy to Clipboard Toggle word wrap

    For example, the following changes the weight of the /dev/sda device in the liftrul VM to 500. 

    # virsh blkiotune liftbrul --device-weights /dev/sda, 500
    Copy to Clipboard Toggle word wrap

13.5.2. Disk I/O throttling in virtual machines
Copier lien

When several VMs are running simultaneously, they can interfere with system performance by using excessive disk I/O. Disk I/O throttling in KVM virtualization provides the ability to set a limit on disk I/O requests sent from the VMs to the host machine. This can prevent a VM from over-utilizing shared resources and impacting the performance of other VMs.

To enable disk I/O throttling, set a limit on disk I/O requests sent from each block device attached to VMs to the host machine.

Procédure

  1. Use the virsh domblklist command to list the names of all the disk devices on a specified VM. 

    # virsh domblklist rollin-coal
Target     Source
------------------------------------------------
vda        /var/lib/libvirt/images/rollin-coal.qcow2
sda        -
sdb        /home/horridly-demanding-processes.iso
    Copy to Clipboard Toggle word wrap

  2. Find the host block device where the virtual disk that you want to throttle is mounted.

    For example, if you want to throttle the sdb virtual disk from the previous step, the following output shows that the disk is mounted on the /dev/nvme0n1p3 partition. 

    $ lsblk
NAME                                          MAJ:MIN RM   SIZE RO TYPE  MOUNTPOINT
zram0                                         252:0    0     4G  0 disk  [SWAP]
nvme0n1                                       259:0    0 238.5G  0 disk
├─nvme0n1p1                                   259:1    0   600M  0 part  /boot/efi
├─nvme0n1p2                                   259:2    0     1G  0 part  /boot
└─nvme0n1p3                                   259:3    0 236.9G  0 part
  └─luks-a1123911-6f37-463c-b4eb-fxzy1ac12fea 253:0    0 236.9G  0 crypt /home
    Copy to Clipboard Toggle word wrap

  3. Set I/O limits for the block device using the virsh blkiotune command. 

    # virsh blkiotune VM-name --parameter device,limit
    Copy to Clipboard Toggle word wrap

    The following example throttles the sdb disk on the rollin-coal VM to 1000 read and write I/O operations per second and to 50 MB per second read and write throughput. 

    # virsh blkiotune rollin-coal --device-read-iops-sec /dev/nvme0n1p3,1000 --device-write-iops-sec /dev/nvme0n1p3,1000 --device-write-bytes-sec /dev/nvme0n1p3,52428800 --device-read-bytes-sec /dev/nvme0n1p3,52428800
    Copy to Clipboard Toggle word wrap

Informations complémentaires

  • Disk I/O throttling can be useful in various situations, for example when VMs belonging to different customers are running on the same host, or when quality of service guarantees are given for different VMs. Disk I/O throttling can also be used to simulate slower disks.
  • I/O throttling can be applied independently to each block device attached to a VM and supports limits on throughput and I/O operations.
  • Red Hat ne prend pas en charge l'utilisation de la commande virsh blkdeviotune pour configurer la limitation des E/S dans les machines virtuelles. Pour plus d'informations sur les fonctionnalités non prises en charge lors de l'utilisation de RHEL 9 en tant qu'hôte de VM, voir Fonctionnalités non prises en charge dans la virtualisation RHEL 9.

13.5.3. Enabling multi-queue virtio-scsi
Copier lien

When using virtio-scsi storage devices in your virtual machines (VMs), the multi-queue virtio-scsi feature provides improved storage performance and scalability. It enables each virtual CPU (vCPU) to have a separate queue and interrupt to use without affecting other vCPUs.

Procédure

  • To enable multi-queue virtio-scsi support for a specific VM, add the following to the VM’s XML configuration, where N is the total number of vCPU queues: 

    <controller type='scsi' index='0' model='virtio-scsi'>
   <driver queues='N' />
</controller>
    Copy to Clipboard Toggle word wrap
Retour au début
Red Hat logoGithubredditYoutubeTwitter

Apprendre

Essayez, achetez et vendez

Communautés

À propos de la documentation Red Hat

Nous aidons les utilisateurs de Red Hat à innover et à atteindre leurs objectifs grâce à nos produits et services avec un contenu auquel ils peuvent faire confiance. Découvrez nos récentes mises à jour.

Rendre l’open source plus inclusif

Red Hat s'engage à remplacer le langage problématique dans notre code, notre documentation et nos propriétés Web. Pour plus de détails, consultez le Blog Red Hat.

À propos de Red Hat

Nous proposons des solutions renforcées qui facilitent le travail des entreprises sur plusieurs plates-formes et environnements, du centre de données central à la périphérie du réseau.

Theme

© 2025 Red Hat