.svg)
- Error
- Cause
- How Do I Check Disk Sector Sizes?
- Solution
Error
The 'Incompatible disk selected' error message can be displayed when attempting a restore or clone operation:
This error will only be displayed when the destination disk of the restore or clone is incompatible, as discussed below; it does not affect disks that are being used to store image and backup files.
Cause
This error indicates that the target disk has a larger sector size than the source, or a USB disk enclosure is changing the reported sector size of the disk, which is not supported.
The table below shows compatible disks for the source and target of restore and clone operations:
| Source Sector Size | Target Sector Size | Compatible |
| 512 or 512e | 512 or 512e | Yes |
| 512 or 512e | 4096 | No |
| 4096 | 512 or 512e | Yes |
| 4096 | 4096 | Yes |
What is a Disk Sector?
A sector is the smallest addressable block on a disk, and until recently, all disks had a sector size of 512 bytes. With the advent of larger, multi-terabyte disks, the physical sector size has increased on some disks to 4096 bytes. These are sometimes referred to as "4K sector disks". To overcome Windows compatibility issues, the majority of disks use a technology called Advanced Format 512e. This enables 4K disks to emulate 512-byte sector size disks by providing an emulated sector size of 512 bytes.
So What's the Problem?
The NTFS file system contains a data structure called the Master File Table (MFT). The MFT is critical to the file system and defines all the files and directories. The MFT contains records, and each record is 1024 bytes (1K) long if the disk sector size is 512 bytes. For a 512-byte per sector disk, this equates to 2 sectors. If the entire file system is restored or cloned to a disk with a sector size of 4096 bytes, then each MFT record (at 1K) would be a quarter of a sector. Since a sector is the smallest amount of data that can be read or written to a disk, this means that NTFS cannot directly read its own data. 4K disks that support Advanced Format 512e do not have this problem, as these disks permit direct access to 512 bytes of data.
How Do I Check Disk Sector Sizes?
To check the sector size of a disk, use the 'System Information' tool. This can be accessed by using the key combination Windows Key + R. In the search bar that opens, search 'msinfo32':
On the left-hand side of 'System Information', expand the 'Components' dropdown menu, then expand 'Storage' and select 'Disks':
A list of the locally attached disks will be displayed in the right-hand window. The 'Bytes/Sector' field shows the sector size of the disk:
Note: Disks with a physical sector size of 4096 bytes that implement 512e will be shown as 512.
Solution
There are no disks currently available that would cause this issue when connected to the system directly (i.e., not using a USB adapter).
We have identified that a number of recent USB enclosures will "fake" being a 4096-byte-per-sector disk and cause the error above. This happens regardless of the actual sector size of the attached disk and whether the disk supports 512e.
Why Do They Do This?
Normally, disks with 512 bytes per sector that are larger than 2TB would need to be initialized using the GUID Partition Table (GPT) format. GPT disks are not supported by Windows XP; however, MBR disks are supported by all Windows operating systems, including Windows XP.
If the reported sector size is changed to 4096 bytes, then MBR disks can be as large as 16 Terabytes and still be accessible by Windows. So, by changing the reported disk sector size to 4096 bytes for disks attached to the enclosure, this enables all Windows operating systems from XP onwards to be able to access disks greater than 2TB. If you are selling USB enclosures, then this gives you a larger potential market and is a "no-brainer" product feature.
Isn't This Good?
Yes, if the only purpose for the USB enclosure is to provide additional storage, and you do not intend to take out the disk. But this is bad if you intend to clone to a disk in the enclosure and then use the cloned disk to boot your PC. It simply won't work. If you remove the disk from the enclosure, then it cannot be read. This is because the sector size will change, and the partition structures on the disk will be unreadable.
Solution for the Error
If you receive the 'Incompatible disk selected' error and you are using an external USB enclosure, then either try a different enclosure that doesn't change the reported disk sector size or directly attach the disk to a port on the system's motherboard. This will ensure that the disk manufacturer's drive geometry is reported correctly and may allow you to proceed with your clone or restore operation, provided that the reported sector size is now compatible.