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VSS_E_ASRERROR_MISSING_DYNDISK
A disk required by a dynamic volume is missing. A critical dynamic volume described by the backup depends on a dynamic disk that the current system cannot access. Dynamic volumes can span or mirror data across multiple members, so visibility of one member is not proof that the volume is reconstructable.
The documented condition is: “The backup failed due to a missing disk for a dynamic volume. Ensure the disk is online and retry the backup.”
Where VSS_E_ASRERROR_MISSING_DYNDISK appears
The failure occurs while the ASR writer or requester evaluates critical-volume topology for backup or restore. The operation needs a coherent view of the dynamic disk group before it can preserve or recreate the volume.
Likely causes
- A SAN LUN, physical drive or virtual disk that belongs to the dynamic disk group is not attached.
- The disk is attached but remains offline, foreign, failed or hidden behind an unavailable storage path.
- The recovery environment lacks the controller driver needed to enumerate one member.
- Disk-group metadata names a member that was removed without first repairing or reconfiguring the dynamic volume.
Evidence to capture before changing storage
- Capture DiskPart disk and volume lists, including dynamic, missing, offline and foreign states.
- Record the dynamic volume type and the members/extents expected from backup metadata.
- Collect storage-controller, multipath and System events around device arrival.
- Identify whether the operation is backup discovery or restore reconstruction; the safe corrective action differs.
Diagnostic sequence
- Match dynamic-disk identities, not only drive letters, because letters can change in recovery.
- Bring a known member online only after confirming it belongs to the intended disk group.
- Check cabling, SAN zoning, virtual-machine disk attachment and storage drivers.
- Avoid deleting a “missing” member until the effect on spanned, striped, mirrored or RAID-5 volumes is understood.
Recovery and retry
Restore visibility of the missing member or redesign the recovery plan to a supported complete topology. Once all required dynamic disks are online and stable, start a new VSS/ASR operation so metadata is gathered again.
What this HRESULT does not prove
The HRESULT does not say that the visible member is corrupt and does not mean that a basic disk with the same size can automatically replace the missing dynamic member.
Difference from nearby VSS results
VSS_E_ASRERROR_NO_PHYSICAL_DISK_AVAILABLE reports absence of any usable fixed disk. This value is narrower: a particular dynamic-volume topology has an absent member.
Practical example
A mirrored dynamic system volume uses two virtual disks, but only one VHD is attached in the recovery VM. The remaining member appears healthy in DiskPart, yet ASR rejects the incomplete disk group with this code.
Guidance for backup software and telemetry
Telemetry should include disk-group identity and missing-member details. Logging only the mounted volume obscures why ASR cannot accept an apparently accessible filesystem.
Official Microsoft references
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