Migrating Enterprise VMware Workloads to Oracle Linux KVM (OLVM 4.4): Disk Conversion & Virtio Kernel Tuning

Symptom & Boot Diagnostics

After converting a VMware VM virtual disk to QCOW2 and importing into OLVM, the VM fails to boot, hanging at the initial ramdisk stage:

[   14.209124] dracut-initqueue[412]: Warning: dracut-initqueue timeout - starting timeout scripts
[   14.891002] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

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Root Cause Analysis

VMware guests utilize SCSI drivers (mptspi or pvscsi). OLVM KVM hypervisors require Linux guest virtio_blk and virtio_net drivers compiled into the initramfs image. If the virtio modules are not included prior to migration, the kernel cannot mount the root filesystem on /dev/vda1.

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Step-by-Step Migration Runbook

Step 1: Inject Virtio Drivers into Guest (Before Shutdown)

On the running VMware guest node, update dracut configuration:

# Add virtio modules to dracut configuration
echo 'add_drivers+=" virtio_blk virtio_net virtio_pci virtio_scsi "' > /etc/dracut.conf.d/virtio.conf

# Rebuild initramfs for current kernel
dracut -f -v /boot/initramfs-$(uname -r).img $(uname -r)

Step 2: Convert VMDK Disk Image to QCOW2

On the migration host or staging storage server:

# Convert flat vmdk file to qcow2 format with preallocation
qemu-img convert -p -f vmdk -O qcow2 -o preallocation=metadata \
  /storage/vmware/guest_disk-flat.vmdk \
  /storage/olvm/guest_disk.qcow2

Step 3: OLVM Host Memory & Swappiness Tuning

Configure KVM host kernel parameters to prevent guest memory starvation:

# Set host swappiness to 10
sysctl -w vm.swappiness=10

# Disable Transparent Huge Pages (THP) on OLVM hypervisor nodes
echo never > /sys/kernel/mm/transparent_hugepage/enabled
echo never > /sys/kernel/mm/transparent_hugepage/defrag

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Sanitized Log Verification

Run the DBPros collector script locally to sanitize host telemetry before submitting diagnostic bundles:

node ./scripts/collector/dbpros-sanitize-collect.js --input-log /var/log/messages

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