So I've just had an external hard drive (5TB Seagate Backup Plus Portable) fail on me, the 3rd such time in 5 years. This is not unexpected behaviour in my experience: each of these hard drives has been read & written from basically 24/7, has failed at a point with less than 10% free space available, and I am always adding more data to them.
I back up all of my data via Time Machine to a second external hard drive (8TB Seagate Backup Plus Desktop), which I've had for about 5 years now; it is still working, despite having run out of storage space on two prior occasions, necessitating some cleaning up of old backups. A checkup with Disk Utility reveals no problems.
I am looking at replacing the failed hard drive with a larger one, which will necessitate buying a desktop drive, since no manufacturer currently makes a 6TB+ USB powered hard drive (except LaCie, but that drive is USB-C powered, and I only have regular USB 3.0 ports). My plan is to purchase a 10TB desktop drive, as 8TB desktop drives are not available in stores where I live at the moment.
The question is:
- Can a 10TB drive be backed up via Time Machine to an 8TB drive if it is only partially full (in this case, roughly 4.5TB of data)?
- If so, how long can I expect the 8TB drive to last if it continues to be used almost entirely for backups? (In the best case scenario, I would need to be able to continue using it for 2 to 3 years until data needs force me to get a larger one.)