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Unexpected AF disk size

EatonEaton Member Posts: 6

I have an AF 512e disk that is 4 TB. I've noticed that there appears to be something odd about the length. In bytes, it is 4000797859328. (That's what IOCTL_DISK_GET_LENGTH_INFO returns via DeviceIoControl.)

The issue is that 4000797859328 mod (%) 4096 is 3584, meaning the disk is not evenly composed of 4096 physical byte sectors. I don't understand why this is the case, it seems extremely odd, and now I would need to add special handling to read the end of the disk, when reading using the 4k sector size.

Does anyone know why this is the case? Is it mentioned in any Advanced Format documentation?

One theory I had was that maybe the HPA and/or DCO may have restricted a few sectors, but that still means operating systems and other software would need to have special handling. Are there any examples of this in action anywhere?


  • EatonEaton Member Posts: 6

    Update - turns out the missing sector data can be read past the end of the disk if it is forced. Looks like it contains some interesting information - anyone know what it is? I was under the impression HPA and DCO cannot be read without special ATA commands, so is this something else?

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