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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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    • Yes
    • virt-storage Sprint 4, virt-storage Sprint 6
    • Bug Fix
    • Hide
      .The `--migrate-disks-detect-zeroes` option no longer fails for VM migration
      Before this update, when migrating virtual machines (VMs) on RHEL 10, the `--migrate-disks-detect-zeroes` option might not have worked, and the migration might have proceeded without zeroed block detection on the specified disk. This problem was caused by a bug in QEMU where mirroring jobs relied on punching holes, resulting in a sparse destination file.

      With this release, QEMU has been fixed to preserve sparseness if the destination system reports that it reads all zeroes, and when no extra effort is made to further sparsify the image. As a result, the `--migrate-disks-detect-zeroes` option works as expected for VM migration.
      Show
      .The `--migrate-disks-detect-zeroes` option no longer fails for VM migration Before this update, when migrating virtual machines (VMs) on RHEL 10, the `--migrate-disks-detect-zeroes` option might not have worked, and the migration might have proceeded without zeroed block detection on the specified disk. This problem was caused by a bug in QEMU where mirroring jobs relied on punching holes, resulting in a sparse destination file. With this release, QEMU has been fixed to preserve sparseness if the destination system reports that it reads all zeroes, and when no extra effort is made to further sparsify the image. As a result, the `--migrate-disks-detect-zeroes` option works as expected for VM migration.
    • 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-target-9.6
          2.39 MB
        2. virtqemud.log-target-9.5
          3.11 MB
        3. virtqemud.log-source-9.6
          3.74 MB
        4. virtqemud.log-source-9.5
          2.26 MB

              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:
                Resolved: