HRESULT 0x803100A7 (FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY

Status / error code:

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Constant name:

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Operating System:

Description:

The required authentication key length is not supported by the drive.

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FVE_E_WIPE_NOT_ALLOWED_ON_TP_STORAGE	FVE_E_NO_EXISTING_PASSPHRASE

FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE

Why this is not a generic disk error

The practical meaning of FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE is that the self-encrypting drive cannot use the authentication key length required by BitLocker for hardware encryption. The HRESULT is 0x803100A7.

Three decisions before remediation

Is the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE target correct?: For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, use the volume or protector GUID and confirm its role; do not rely only on a drive letter or friendly name.
Is the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE request allowed?: For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, resolve effective policy, Windows edition, caller token and management source for the hardware-encrypted drive negotiation operation.
Is the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE state stable?: For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, record conversion, protection, lock and reboot status before modifying anything.

For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, note: Hardware-encrypted drives add firmware, storage-driver and drive-security state below the normal BitLocker volume provider. When diagnosing FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, remember: BitLocker can reject the hardware path before conversion starts, and policy may or may not permit a fallback to software encryption. For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, note: If policy permits software fallback, verify the final method explicitly. When diagnosing FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, remember: A failed hardware dry run can otherwise leave an administrator assuming protection that never started.

Why a common workaround is wrong

This should not be diagnosed as a missing eDrive capability or policy disallowing hardware encryption; the drive was considered but key parameters are incompatible. For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, that nearby condition needs a different corrective action and may produce a similar user-facing message.

Confirm the returning layer

For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, record drive model/firmware, hardware-encryption status, supported key sizes, storage driver, policy algorithm and dry-run result. For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, keep the full HRESULT and the first method that returned it because later cleanup calls can report a different state.
For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, capture manage-bde -status and the protector inventory for the exact volume GUID, not only the drive letter, because letters can change in WinRE, clusters and deployment environments.
Export BitLocker operational events for the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE failure and note the boot session, caller identity and management source; that evidence separates this BitLocker condition from a generic access or storage error.

manage-bde -status
powershell -NoProfile -Command "Get-CimInstance -Namespace root/cimv2/security/MicrosoftVolumeEncryption -Class Win32_EncryptableVolume"

Correct the configuration deliberately

For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, update supported firmware or use BitLocker software encryption; do not weaken key requirements to fit the device.
After correcting the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE prerequisite, refresh protection, conversion and lock state before one controlled retry; a cached UI message is not proof that the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE condition is still active.
Before a FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE remediation deletes protectors, changes firmware mode, resizes partitions or decrypts a production drive, verify that an independent recovery method is available and escrowed in the intended directory or account.

Treat FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE as a state label rather than a complete recovery plan. Confirm a successful retry with an updated BitLocker state query and a verified recovery path.

State checks specific to FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE

Checkpoint	How to interpret it for FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE
Before the call	Record the target identity and the pre-call hardware-encrypted drive negotiation state. For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, the decisive boundary is that the self-encrypting drive cannot use the authentication key length required by BitLocker for hardware encryption.
At failure	Preserve drive model/firmware, hardware-encryption status, supported key sizes, storage driver, policy algorithm and dry-run result. This proves whether FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE came from BitLocker itself or from a wrapper translating another result.
After correction	Update supported firmware or use BitLocker software encryption; do not weaken key requirements to fit the device. The FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE request should then advance without removing an unrelated recovery route.
After reboot or remount	Recheck protection, conversion and lock state for FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE; a successful management call is incomplete if the next boot cannot unlock the volume.

Verification after the change

For FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE, success means more than the absence of a dialog. Confirm that the condition represented by FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE now matches the intended design, that the protector inventory has not lost an independent recovery route, and that the next reboot or remount can unlock the volume. If the FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE request advances to another HRESULT, record both values in order because that transition reveals the next unmet prerequisite.

References

Reference set for FVE_E_KEY_LENGTH_NOT_SUPPORTED_BY_EDRIVE:

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