I recently saw a youtube video about refreshing backup files on HDD (external,in my case),but unfortunately,the video was for windows.Since I have Never refreshed my backup external HDD,I think it is probably time.I have converted all my other HDDs to Ext4, but my external backup is still NTSF BECAUSE I don't have a big enough HDD(spare) to copy the data to.Is there a linux program that will refresh the files without copying them?I am running Ubuntu 16.04 on my main tower.I do have all the important stuff backed up on DVDs,so I could spend a day copying them back onto the backup drive.I hope there is an easier way!!

How did you create the backup in the first place?
Is it a true backup, or only a copy?
What things did you back up? If not the whole system, then what file systems, folders, or partitions?

Linux is not windows, and I have not seen that video, but in general linux is not very much like windows and backups are an entire different book!

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Sorry for being so vague.They are only copies of data files,originally copied from Windows machine.They are all still intact,but I am concerned about data fade,as some of the files have been on that HDD for years without being refreshed or re-copied.I am also wondering if data fade due to age is dependent on file format;ie is it less of an issue on Ext4 than on NTSF?Since I always use a separate SSD for my boot drive,and a HDD for data,I no longer bother with a system backup.All of the data is duplicated on 2 computers as well as the external HDD and a stack of DVDs.Just did some more googling for "bit rot"etc.Sounds like a can of worms to me.Some say data fade/bit rot is no longer an issue or never was(like global warming).Guess I will keep the DVDs in a safe place and pray!!

To refresh the bits on a hard drive:That will read the disk and write it back exactly as it was.

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Thanks AwesomeMachine.I saw a reference to this somewhere.Just what I need.

You're welcome.

That may give you some confidence re the state of the physical device, but does nothing to validate the actual data.
You have to (at least) read the data to know if it is useful. For long term storage I tend to use fsarchiver as it validates all the data individually. Doesn't stop bitrot, but at least you know about it when you go to retrieve the file.
I would be a lot less sanguine about the DVDs - they are much more likely to degrade than an idle disk I would imagine.

If you have backups only on one media or device then you are one failure away from having no backups. The importance of this usually strikes on the day that you need your backup and discover it picked THAT day to fail.

On the other hand, hard drive lifetimes are measured by usage (reads, writes, spins, hours of operation, etc. depending up technology involved) so a drive that is only powered up for a backup or restore event might last a very long time with any luck. Still ... I would have a plan for if that drive fails. (secondary backups to DVD media, tape, or offsite storage might be options)