3 is not reinstalled? As Scott has noted in this topic's OP, the Windows 10 upgrade process may add a partition by reclaiming space after the OS ("C:") partition on your hard drive. =hankfoner - My question is: If I ever have to do an Image Backup Restore will it matter that partiton no. It may be simpler to delete the old backups manually. Use your judgement as to which option is right for you. By changing the setting you can have retention purge image files in that folder regardless of the data the image backups contain. This option determines how Reflect handles retention conflicts when you have backups from different sources going to the same target folder (which is effectively what has happened here with the resizing of the C: partition). Solution: Where it says "Retention Rules Apply To" you can change the option to All backup sets in the target folder.
Where it says "Retention Rules Apply To", if you have this set to Similar backup sets in the target folder, then new backups created post-Windows 10 upgrade may not be purged as the new backups look to be dissimilar i.e. Depending on your Reflect settings you may notice that Retention does not behave as expected In the Macrium Reflect Defaults there is an option under the Backup settings called Retention Rules. You should modify your XML definition to include this new partition to ensure that you can recover your system successfully. However, this will not include the new Windows 10 partition.
Solution: Reflect will handle this automatically by creating a new full backup. Incremental / Differential backup sets will not be able to append to chains from before the upgrade. Windows 10 is adding an extra partition to many users' systems as part of the upgrade process. It does this by reclaiming data from the end of C.