sureshanaparti commented on code in PR #640:
URL:
https://github.com/apache/cloudstack-documentation/pull/640#discussion_r3062139036
##########
source/adminguide/virtual_machines/importing_vmware_vms_into_kvm.rst:
##########
@@ -117,6 +117,178 @@ If you are hitting the following error when running
ovftool, install the depende
dnf install libnsl
+VDDK-based Optimized Conversion
+-------------------------------
+
+CloudStack supports an optimized VMware-to-KVM migration path using virt-v2v
in vpx input mode combined with
+VMware's Virtual Disk Development Kit (VDDK). This method eliminates the OVF
export phase entirely and streams
+disk blocks directly from the source hypervisor into the conversion pipeline,
resulting in significantly faster
+migration times.
+
+The traditional OVF-based workflow operates in two sequential phases:
+
+1. Export the entire VM as OVF/VMDK files to temporary storage (full disk
copy).
+2. Convert the local VMDK files using virt-v2v (second full disk read and
write).
+
+The VDDK-based workflow replaces both phases with a single streaming pipeline:
+
+- virt-v2v connects directly to vCenter via ``vpx://``
+- Disk blocks are read on demand via VDDK (using nbdkit internally as the
translation layer between the
+ VDDK API and virt-v2v's NBD block device interface)
+- Conversion and disk transfer happen concurrently
+- Only allocated blocks are transferred; zero-filled and sparse extents are
skipped
+- No intermediate OVF or VMDK files are created
+
+This reduces disk I/O amplification, eliminates temporary staging storage, and
shortens end-to-end migration time.
+
+.. note:: CloudStack does not distribute VDDK, operators must download it
separately.
+Along with the new VDDK-based conversion method the traditional OVF-based
method remains supported for environments.
+Operators can choose the conversion method on a per-migration basis in the UI
import wizard.
+
+Host Prerequisites for VDDK-based Conversion
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+To use VDDK-based migration, operators must prepare each KVM host that will
run the conversion: install the conversion
+tools, install VDDK manually, configure libguestfs, and verify host
connectivity to vCenter/ESXi.
+
+Example: prepare one KVM conversion host
+
+**Step 1: Install the conversion stack (RHEL / Rocky / Alma Linux)**
+
+::
+
+ dnf install -y epel-release
+ dnf config-manager --set-enabled crb
+ dnf install -y virt-v2v libguestfs-tools libguestfs-xfs qemu-img nbdkit
+
+**Step 2: Configure libguestfs backend as** ``direct``
+
+VDDK does not work with the default sandbox backend. Configure ``direct``:
+
+::
+
+ cat <<EOF > /etc/profile.d/libguestfs.sh
+ export LIBGUESTFS_BACKEND=direct
+ EOF
+
+ source /etc/profile.d/libguestfs.sh
+
+This can also be configured persistently with ``libguestfs.backend`` in
``/etc/cloudstack/agent/agent.properties`` (see `Agent Properties for
VDDK-based Conversion`_ below).
+
+**Step 3: Download and install VDDK**
+
+Download the VDDK tarball and extract it to a known location on the KVM host,
for example, ``/opt/vmware-vddk``.
+The resulting directory must contain the VDDK libraries under a ``lib64``
subdirectory.
+
+::
+
+ mkdir -p /opt/vmware-vddk
Review Comment:
is this default path for vddk (expected by nbdkit)?
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