Checksum test of NAS backup to external HD

Hi

I think it would be very good to have the option to do checksum test of backup from NAS to external HD.

In this way one could be more certain that once the file is on the NAS (with bit-rot protection enabled) then

any future backup would keep the data integrity. 

Naturally we do incremental backup of the NAS to external HD and therefore checksums should be done

on the incremental backups.  

If the useer now and then would like to make a total check of the correctnes of the backup using checksum test

that should be possible too. I guess this would be faster than making a new backup.

To make this service complete it would be good to offer checksum test also for:

- transfer of files via USB to the NAS typically for uploading new photos from SD-card etc

- backup function from Mac/PC to the NAS that ensures the checksum is ok

  - could be that Acronis backup software for Windows already do that, but I am not sure.

This checksum test should preferably run in the background since it may take some time.

If backup is done to another ReadyNAS under OS6 that may be easier to implement - but I am not sure.

The normal usage of NAS I think is that files uploaded on the NAS will be read within some limited time

and possible corruption seen. Backups that get corrupted is much harder to detect I think. 

Therefore I would set first priority on making a function to check the correctness of backup

of the NAS to external HD.