[SOLVED] File transfer between SSD and HDD has SSD speed for first few seconds

[andreitc]

Hello,
I discovered something on file transfers between storage devices and I wanted to know why this is happening (just for my curiosity)

I have an SSD and a Hard Drive, both on Sata 3 standard. The SSD has about 500MB/s transfer speed and the HDD has about 50MB/s.

However, when I want to transfer a file from the SSD to HDD something weird happens.
For the first few seconds (about 5 to 10) the transfer speed is the speed of the SSD (about 500MB/s), after that, the speed drops to the speed of HDD (about 50MB/s).
Obviously, I know that the speed of transfer should be the minimum between the two devices, (although the ssd is capable of transferring at 500mb/s, the hdd will handle max 50mb/s so the transfer speed will be 50mb/s), but why is that in the first few seconds the speed is the one the ssd is capable of sending? How can the information be written to the HDD at 500MB/s for a short period of time, if it is only capable of sending/receiving at 50mb/s) ?

Thanks. This is a picture to illustrate the phenomenon:

 

[AJNameS]

Most likely just the software/system is not as sensitive as u think. I've seen such 'phenomenons' many times. Sometimes the software, after some more loops, starts to measure the correct values. Just see what a non-calibrated system can make with a laptop battery - it may think u have 30-40% remaining, but u may find it over after just 10 minutes. And after some battery loops, it starts to have a much bigger accuracy.

 

[popatim]

Seems to be about 250MB/s peak which is probably the drives cache filling up.

 

[USAFRet]

Hello,
I discovered something on file transfers between storage devices and I wanted to know why this is happening (just for my curiosity)

I have an SSD and a Hard Drive, both on Sata 3 standard. The SSD has about 500MB/s transfer speed and the HDD has about 50MB/s.

However, when I want to transfer a file from the SSD to HDD something weird happens.
For the first few seconds (about 5 to 10) the transfer speed is the speed of the SSD (about 500MB/s), after that, the speed drops to the speed of HDD (about 50MB/s).
Obviously, I know that the speed of transfer should be the minimum between the two devices, (although the ssd is capable of transferring at 500mb/s, the hdd will handle max 50mb/s so the transfer speed will be 50mb/s), but why is that in the first few seconds the speed is the one the ssd is capable of sending? How can the information be written to the HDD at 500MB/s for a short period of time, if it is only capable of sending/receiving at 50mb/s) ?

Thanks. This is a picture to illustrate the phenomenon:

That first few seconds is just the cache of the HDD. Once it fills up, the transfer speed reduces to the write speed of the HDD.

Performance depends on the speed of the slowest device in the chain. Here, the HDD.