Question: When moving big files from a SSD to a HDD on my local computer, I sometimes see the first part of a big file (several GB) being moved in literally milliseconds. However, I haven’t been able to make a picture of that until now:
Please note that the size of the file being moved is about 4.4 GB.
Now the question is: Is Windows (10 x64) showing me correct progress updates, and if yes, how can write speeds that high be possible with an ordinary, now several years old HDD?
Information:
- HDD in use : ST3250312CSS
- SSD in use : Kingston SSD SV300 (seq. write / read at about 450 MB / s)
Answer: It is using the HDD cache (i.e. memory).
The SSD has high read speed and fills up the cache on the HDD.Once there is data, it starts to write – but it is not writing at the rate it is receiving.
Once the cache is full and the HDD is unable to clear it by writing fast enough, the speed drops to the more normal speed expected of a HDD.