PowerProtect: VM Backup Warning: Misalignment Detected in Write to Byte Offset
Summary: When performing VM backups using PowerProtect with the Virtual Machine Direct Engine, warnings appear indicating misalignment during write operations. Backups complete successfully but report errors related to block alignment. ...
Symptoms
The PowerProtect appliance is used to protect the vSphere environment with the Virtual Machine (VM) Direct Engine solution. The VM Backup is generating messages indicating there is a Misalignment detected in write to byte offset for several blocks.
- Backup job completes with status: Successful with errors.
- Warning messages in logs are similar to
YYYY-MM-DDT15:45:42.290Z WARN: [8044cfeead4da4a7;96324e02977e7f59] Virtual machine does not support Change Block Tracking, only full backups can be performed.
...
YYYY-MM-DDT15:45:42.730Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] CBT data not available: Synthesizing used block list to cover entire logical disk.
...
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "ExcludedObjects": [
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] {
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "Type": "FILE_SYSTEM_FILE",
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "Id": "C:\\pagefile.sys"
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] },
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] {
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "Type": "FILE_SYSTEM_FILE",
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "Id": "C:\\hiberfil.sys"
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] },
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] {
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "Type": "FILE_SYSTEM_FILE",
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] "Id": "C:\\swapfile.sys"
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] }
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] ]
YYYY-MM-DDT15:45:37.679Z NOTICE: [8044cfeead4da4a7;96324e02977e7f59] },
...
YYYY-MM-DDT16:11:38.222Z INFO: [8044cfeead4da4a7;96324e02977e7f59] Data Mover: Hard disk 1: FSS 8 KB: Misalignment detected in write to byte offset 68367343104 with length 1048576 bytes.
...Cause
The issue occurs due to a combination of VM and policy settings:
- VM does not support Change Block Tracking (CBT).
- Protection Policy uses Performance Backup Optimization (FSS).
- Policy excludes swap files from backup.
- Windows partition uses 4 KB block size.
Because CBT is unavailable, the backup synthesizes an in-use block list spanning the entire disk. This structure is not initialized with FSS 8 KB alignment. When swap file exclusions are applied, the list fragments into multiple regions aligned to 4 KB blocks, conflicting with FSS requirements. Normally, the block list is realigned after exclusions, but a bug prevents this because the initial structure lacks 8 KB alignment.
Additional constraint: VMs with virtual hardware version older than 7 cannot support CBT.
Resolution
This behavior does not affect backup integrity. A fix is planned for a future release (>19.22).
Workaround:
- Upgrade the VM hardware version to 7 or later and enable CBT, or
- Disable the Exclude swap files in backup option in the Protection Policy.
Additional Information
Additional Information
- Affected component: Virtual Machine Direct Engine backups with FSS optimization
- No data loss occurs; backups remain valid
- Future fix planned under ID PDM09I-1970