Disk speed issue?

Hi. Accidentally I imported one file from "backup" drive, and second from main drive. Both disks are HDD, "main" is 7200 rpm, "backup" 5400. I checked them in crystaldiskmark and faster get's 139 MB/s, slower about 130MB/s read speed. Backup disk is plugged via USB3.0, from disk station dock.
BUT
From "backup" drive render speed was 120fps, but "main" disk was 40.
After render I replaced file twice, from backup to main and run render. This same file. Why this big difference?

PS. Usually I copy all current project files to m2 ssd drive, so disk speed should not be a bottle neck at all...?

If you render to the same spinning disk that the sources are coming from, I'd expect it to be slower on an otherwise strong machine.

Yeah, im aware of that. Render was set to other m2 disk.

Many things can affect HDD performance eg maybe the file is badly fragmented on the main drive causing numerous seek operations but contiguous on the backup drive? maybe the file is written to / being read from a slower part of the platter on the one drive vs the other? Hard to say.

I did windows "optimisation" (defragmentation) disk, it look better, but still far from other disk.

Access time plays a big role on HDDs too.
C'mon, it's the age of SSD now.

Also RAM cache plays a difference. And with HDDs, unlike the newer ssds, the speed drops when they are full or close to full. Goes from 250MB/s when empty (newer drive) down to 60ish when its full. If your files are at the end of the drive it could explain the drops in speed.

At the moment I have 1,81 TB free of 5,45TB. I don't know, where physically is placed this source
But to be sure, disk was at last once full.
When I copy from (or to) disk, speed is stable and normal. Same as second disk, which have better performance.
This isn't crucial for me, but devs should know, that this is possible, and for someone could be big deal.