S2D virtual disk extension fails due to sector size mismatch (4Kn vs 512e): how to reconcile differing drive formats?

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S2D virtual disk extension fails due to sector size mismatch (4Kn vs 512e): how to reconcile differing drive formats?

Yone Louis 0

Attempting to extend an S2D virtual disk fails with "Incompatible Allocation Unit Size" when newly added physical capacity drives were formatted using a different sector size (4Kn vs 512e). How do we reconcile physical sector size differences within an active S2D pool?

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Answer 1

Hello Yone Louis,

Storage Spaces Direct requires all physical disks in a pool to use the same sector format. If a virtual disk was created on 512e drives, it cannot be extended across 4Kn drives because the sector sizes differ, and Windows will stop the operation with an incompatible allocation unit error. In practice, you cannot mix these two layouts within the same virtual disk.

The supported approach is to retire the 4Kn drives from the pool using Set‑PhysicalDisk -Usage Retired, replace them with disks that match the 512e format, and then run Repair‑VirtualDisk to restore consistency. If your hardware vendor provides a utility that allows sector reformatting, you can reformat the new drives offline to 512e before adding them back.

Once all disks in the pool share the same sector specification, you can safely extend the storage by running Resize‑VirtualDisk followed by Resize‑Partition. If this resolves the issue and restores your environment, please accept this answer.

Tracy Le.