We installed a new 5TB WD USB drive for backups on one of our client's servers last week. We had gotten a good deal on the gaming drive, but did not realize that the gaming drives come pre-formatted as ExFAT.
The backup plan speed would go from extremely slow to very fast, then back to very slow. After three days it had only backed up half of the files. Our top tech determined that the drive was great when writing large files but absolutely TERRIBLE when backing up/copying files under 2-3K (apparently a known characteristic). The server has 500,000 of these very small files.
We killed the backup, reformated it as NTFS, and as of now it has already done more in two hours than it did in a full day as ExFAT.
So this is just a heads up to anyone who might find themelves with long running local backups to check the Drive formatting. If EXfat - switch to NTFS.