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  1. RHEL
  2. RHEL-82906

--migrate-disks-detect-zeroes doesn't take effect for disk migration [rhel-9.7]

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    • qemu-kvm-9.1.0-24.el9
    • Yes
    • Critical
    • 2
    • rhel-virt-storage
    • ssg_virtualization
    • 14
    • 14
    • 5
    • False
    • False
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      None

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    • Yes
    • virt-storage Sprint 4, virt-storage Sprint 6
    • Known Issue
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      .The `--migrate-disks-detect-zeroes` option might not work for VM migration

      Currently, when migrating virtual machines (VMs) on RHEL 9, the `--migrate-disks-detect-zeroes` option might not work and the migration might proceed without zeroed block detection on the specified disk. This problem is caused by a bug in QEMU where mirroring jobs had been relying on punching holes, which results in a sparse destination file.
      Show
      .The `--migrate-disks-detect-zeroes` option might not work for VM migration Currently, when migrating virtual machines (VMs) on RHEL 9, the `--migrate-disks-detect-zeroes` option might not work and the migration might proceed without zeroed block detection on the specified disk. This problem is caused by a bug in QEMU where mirroring jobs had been relying on punching holes, which results in a sparse destination file.
    • Done
    • Unspecified
    • Unspecified
    • Unspecified
    • x86_64
    • None

      What were you trying to do that didn't work?
      --migrate-disks-detect-zeroes doesn't take effect for disk migration

      Please provide the package NVR for which the bug is seen:
      libvirt-10.10.0-7.el9.x86_64
      qemu-kvm-9.1.0-15.el9.x86_64
      kernel-5.14.0-569.el9.x86_64

      How reproducible is this bug?:
      100%

      Steps to reproduce:

      1. Set up migration env and start vm on src host with a disk.

# qemu-img create -f raw /var/lib/libvirt/images/raw.img 1G
Formatting '/var/lib/libvirt/images/raw.img', fmt=raw size=1073741824

# virsh edit vm1
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' />
      <source file='/var/lib/libvirt/images/raw.img'>
      </source>
      <target dev='sda' bus='scsi'/>
    </disk>

# virsh start vm1

2. Mount sda and create a file in guest.
# mkfs.xfs /dev/sda
# dd if=/dev/random of=/dev/sda bs=1048576 count=100   
100+0 records in
100+0 records out
104857600 bytes (105 MB, 100 MiB) copied, 0.471111 s, 223 MB/s

3. Check the current disk usage on src host.
# qemu-img info /var/lib/libvirt/images/raw.img -U
image: /var/lib/libvirt/images/raw.img
file format: raw
virtual size: 1 GiB (1073741824 bytes)
disk size: 168 MiB
...

4. Create a disk on the target host.
# qemu-img create -f raw /var/lib/libvirt/images/raw.img 1G
# qemu-img info /var/lib/libvirt/images/raw.img -U
image: /var/lib/libvirt/images/raw.img
file format: raw
virtual size: 1 GiB (1073741824 bytes)
disk size: 1 MiB
...

5. Create migratable xml.
# virsh dumpxml vm1 --migratable > mig.xml
# vim mig.xml
...
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' />
      <source file='/var/lib/libvirt/images/raw.img'>
      </source>
      <target dev='sda' bus='scsi'/>
    </disk>
...


6. Migrate vm with --migrate-disks-detect-zeroes option.
# virsh migrate vm1 qemu+tcp://targethost/system --verbose --live --p2p --copy-storage-all --xml mig.xml --migrate-disks-detect-zeroes sda
Migration: [100.00 %]

7. Check disk usage on target host.
# qemu-img info /var/lib/libvirt/images/raw.img -U
image: /var/lib/libvirt/images/raw.img
file format: raw
virtual size: 1 GiB (1073741824 bytes)
disk size: 1 GiB
...

      Expected results:
      Can retain sparsity with option --migrate-disks-detect-zeroes.

      Actual results:
      --migrate-disks-detect-zeroes doesn't take effect.

      Additional info:

      Tested the following combinations:

          disk format on src host         disk format on target host    test result
         rbd/raw/qcow2          +             rbd                     FAIL
         rbd/raw/qcow2          +             raw                     FAIL
         rbd/raw/qcow2          +             qcow2                   PASS

        1. virtqemud.log-source-9.5
          2.26 MB
          Liping Cheng
        2. virtqemud.log-source-9.6
          3.74 MB
          Liping Cheng
        3. virtqemud.log-target-9.5
          3.11 MB
          Liping Cheng
        4. virtqemud.log-target-9.6
          2.39 MB
          Liping Cheng

              eblake_redhat Eric Blake
              rhn-support-lcheng Liping Cheng
              virt-maint virt-maint
              Aihua Liang Aihua Liang
              Daniel Vozenilek Daniel Vozenilek
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                Created:
                Updated: