Ok, so the secondary drive will have an exact duplicate and a third would hold tombstones?
From the technical brief
"When Windows Home Server Drive Extender migrates a file, it creates the shadow with the same name as the tombstone. To prevent name conflicts, Windows Home Server Drive Extender puts every shadow file under the \DE directory, but it preserves the rest of the path. For instance, if Windows Home Server Drive Extender migrates \photos\poodles.jpg, the shadow file would have the path \DE\photos\poodles.jpg. If the primary hard drive fails, the Migrator service can re-create the tombstones on a new primary hard drive by scanning the files on the secondary hard drives. Continuing with the same example, if the Migrator service is re-creating a new primary data partition, and it finds the file \DE\photos\poodles.jpg on a secondary data partition, the Migrator service can create a tombstone file called \photos\poodles.jpg on the primary data partition and link it to that shadow file. "
So to answer your question, tombstones are on the primary partition but it may also contain data.
From the document again:
To highlight how this works, consider this example. If a new photo is saved to the Photos shared folder on your home server, the following happens:
1. A new entry for this file is created in the file table on the primary data partition. On a home server with multiple hard drives, this is a "tombstone" file.
2. The Windows Home Server Drive Extender file system filter creates a pointer (reparse point) for the new file and determines onto which hard drive the photo should be stored. The tombstone is updated with the location of the actual file. This file is known as the "master or primary shadow."
3. If Folder Duplication is enabled for the Photos shared folder, the Windows Home Server Drive Extender Migrator service creates a duplicate copy of the file and updates the tombstone file on the primary data partition with the reparse point to include the second location of the shadow file. This file is known as the "alternate or secondary shadow."
Lara Jones [MSFT] | Program Manager
Community Support and Beta | Windows Home Server Team
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