Performance expectation Windows SSD -> External USB

I’m new to restic. And I want use it tot backup files stored on an internal NVME ssd to an external USB HDD.

The command I have used is as follow (X: is the external drive and H:\Pictures is on the SSD):

restic -r H:\Restic --verbose backup --use-fs-snapshot --read-concurrency 6 H:\Pictures

24 hours ago I started by backing up pictures. In total 51292 files which are 650 GB in total size. Initially it gave me an ETA of 16 hours. But after 24 hours it still show and ETA of 6 hours.

The machine I’m running this on is a AMD Ryzen 5800x (8 real cores/16 virtual ones). But while backing up, the CPU never goes over 10%. The external disk write speed never exceeds 16 MB/s. If copy files to that same disk, it can achieve around 140 MB/s. Offcourse that’s when copying large files, but that’s only to point out how fast that disk can be.

In Windows I already added restic.exe to the exclusion list of the Windows 11 malware scanner. Both the binary, as the process. And I have also tried to disable the real time virus scanner.

Am I missing something, or is this the performance I should expect?

Most likely this is the reason. CMR type, heavily fragmented with limited free space, some slow filesystem etc. Impossible to guess exact reason. Some large file performance test does not tell you much - could it maintain this value when writing e.g. 650 GB of large files?

On HDD what you can always try is to increase pack size - from default 16MB to something much higher.

Subsequent backups should be much faster (assuming that not much data is added or changing).