prashanthr2 opened a new issue, #13390:
URL: https://github.com/apache/cloudstack/issues/13390
### problem
Live migrating a VM with storage to a SharedMountPoint target pool fails
with:
`LibvirtException: Operation not supported: pre-creation of storage target
for incremental storage migration of disk 'sda' is not supported`
StorageSystemDataMotionStrategy.decideMigrationTypeAndCopyTemplateIfNeeded()
uses supportStoragePoolType() to decide whether to use LinkedClone
(incremental) or FullClone migration. supportStoragePoolType() always includes
SharedMountPoint in its accepted types , the same as NFS. So any volume with a
template_id and a backing file on a SharedMountPoint destination is incorrectly
routed to LinkedClone migration. This sets the libvirt flag
VIR_MIGRATE_NON_SHARED_INC (128), which requires QEMU to pre-create the
destination disk with a backing chain. QEMU does not support this pre-creation
step on SharedMountPoint storage, causing the migration to fail. NFS works
because QEMU can freely create QCOW2 files with backing chains on a flat
filesystem.
The bug does not trigger if template_id is null in the volumes table,
because getVolumeBackingFile() returns null in that case, causing
decideMigrationTypeAndCopyTemplateIfNeeded() to fall through to FullClone,
which uses VIR_MIGRATE_NON_SHARED_DISK (64), a flag QEMU supports on
SharedMountPoint storage.
### versions
4.22.0/4.22.1
### The steps to reproduce the bug
1. Set up a CloudStack KVM environment with a SharedMountPoint primary
storage pool.
2. Deploy a VM from a standard template (ensure the volume has a non-null
template_id and a QCOW2 backing file on the source pool).
3. Add a second SharedMountPoint primary storage pool as the migration
target.
4. Trigger a live migration of the VM with storage to the target pool
(migrateVirtualMachineWithVolume).
5. Observe the migration fails with the error above.
Workaround: Set template_id = NULL in the volumes table for the affected
volumes before migrating. This forces FullClone migration.
### What to do about it?
In
StorageSystemDataMotionStrategy.decideMigrationTypeAndCopyTemplateIfNeeded(),
exclude SharedMountPoint from the LinkedClone path by adding one condition:
```
//engine/storage/datamotion/src/main/java/org/apache/cloudstack/storage/motion/StorageSystemDataMotionStrategy.java
if (StringUtils.isNotBlank(srcVolumeBackingFile) &&
supportStoragePoolType(destStoragePool.getPoolType(),
StoragePoolType.Filesystem) &&
+ destStoragePool.getPoolType() != StoragePoolType.SharedMountPoint &&
srcVolumeInfo.getTemplateId() != null &&
Objects.nonNull(vmTemplate) &&
!Arrays.asList(KVM_VM_IMPORT_DEFAULT_TEMPLATE_NAME,
VM_IMPORT_DEFAULT_TEMPLATE_NAME)
.contains(vmTemplate.getName())) {
```
This forces SharedMountPoint destinations to always use FullClone →
VIR_MIGRATE_NON_SHARED_DISK, which QEMU supports. The template pre-copy step is
also correctly skipped, as it is not needed for a full disk migration.
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