What a VMware MF File Does During VM Migration

An OVF/OVA package usually holds three things: the OVF descriptor file, which defines the VM configuration, one or more VMDK files, which hold the virtual disk data, and the MF file. The MF file lists SHA1 or SHA256 hash values for the OVF and VMDK files, and those cryptographic checksums work like fingerprints.

During an import or a migration, the virtualization platform recalculates the hash values of the OVF and VMDK files and compares them with the ones in the MF file. Matching checksums mean the files arrived intact and unmodified. If they do not match, the import can fail or throw warnings, which stops a corrupted or tampered virtual machine from being deployed.

That check matters most in cross-host migration, transfers between platforms and remote deployments, where files can be corrupted, downloads can stop short and someone can edit a file by hand.

When the MF file is missing or corrupted, the import may still go ahead in some cases, with the integrity check skipped and the risk on you.

The MF file is a checkpoint for security and consistency, and it is how a virtual machine template stays trustworthy through migration and deployment.

Q1: What happens if the MF file is missing?

Some systems still allow the import, with the integrity verification skipped.

Q2: Can I manually edit an MF file?

Only if you regenerate the correct checksums afterwards. Without that, the import throws errors.

Q3: How can I verify MF file contents?

Open it in a text editor and compare the SHA values it lists with the hashes you recalculate.

Q4: Why does OVF/OVA import sometimes fail?

A checksum mismatch, an incompatible version, corruption or a network interruption can cause failures.