Sometimes the scan itself (stage 1 to 3) can take a very long, long time. It would be prudent to have the ability to pause and save the scan process. While I understand their likely is a reason (there is a reason for everything, right?) not many average folk like to keep their computers running 24/7 and I found the scanning can slow down your PC as well. Heck, even cancelling a scan can take a while unless you use the task manager to kill the application.
It would be great if you could throttle the cpu utilization of the recuva application.
And i also support the feature request. Especially of the feature to save the scan (i.e. to an USB drive).
This has been suggested several times before. I think that the main reason why Recuva doesn't have this feature is that the scanned device is volatile, the scan results are more or less obsolete as soon as the scan has completed. I assume (and hope) that Recuva checks that the space occupied by any files selected for secure deletion is still free before it actually overwrites it. If the info is several hours, or days, old then it could be a 'write' mess. (I've been here too long, having to resort to puns.)
Recuva takes time to cancel because a cancel leaves a search list of files found so far, and that takes time to produce. As for taking too long to scan, Recuva was developed when disks were around 150 gb or so. These 3 tb and up disks are just too large for anyone.
I think in most cases the drive, where the files should be recovered, will be attached as a second drive (at least). So from a system point of view there should not be that many changes.
You could create something like an expert mode, where the user needs to know what he is doing. In this mode you can save the list, and continue working with it. And since you are in expert mode, you are doing it at your own risk. It means you really should know what you are going to do.
In the best case Recuva could install a device driver, which makes sure that no clusters are being overwritten by another process. If there are no free clusters, the device driver should report the drive as 100% full.