I have a few HDDs that I intend to use for data backup. The projected use case is a full overwrite of contents every month or so, and I intend to read only in the event of data loss on my primary memory units.
I want these drives to last as long as possible, which is why I plan to only keep the drives connected when I want to write and evaluate health. In my mind, this prevents degradation while protecting from edge-case power surges and device theft. Is this strategy going to do anything to extend lifespan, or am I better off keeping the drives plugged in?
The most important thing you can do, to prolong the life of the HDDs, is to NOT do a full overwrite every month or so. Sync instead.
Do as little as possible to make the contents of the HDD an identical copy of the source.
There are many sync utilities and backup softwares you can use. I use a script and rsync.
Using a sync utility like rsync it is even possible to efficiently make versioned full snapshot backups. Then a new timestamped snapshot backup is created by comparing the previous snapshot with the original. Files that are in the previous snapshot are hardlinked from the previous snapshot, which save time and storage. Only new or modified files need to be copied.
This way it is very fast to create a updated snapshot and, as long as you have not made large changes to the original files, every new snapshot takes up very little storage.
I have two SSDs in my PC. The main SSD is used as normal with the OS, programs and user files. And a secondary SSD holding versioned rsync snapshots of the user files. Every boot a new updated snapshot is automatically created. Also old snapshots are automatically deleted as needed, so at most only 7 daily, 4 weekly and 4 monthly snapshots are retained.
I also have two multibay USB DAS. One primary DAS is used for media files, movies and so on. The primary DAS is also used for manually triggered snapshots of different folders on the main SSD. The secondary DAS is used for rsync snapshot backups of the main DAS. The primary DAS is usually always turned on with the PC. The secondary only now and then to backup the primary DAS.