File transfer speed sometimes 110MB/s and sometimes 45-55MB/S.

Hi all,

Does anyone have an explanation for this:

Yesterday, I installed a new WD20PURZ HDD in a USB3 enclosure and connected it to the USB3 port of my HP630 thin client acting as my home server / NAS. This is the 2nd HDD I connected to this server this way. So there are 2x USB3 HDDs connected to it by USB3 ports. No RAID, nothing fancy. Just 2 separate EXT4 file systems.

OMV is running in a Proxmox Ubuntu Server 20.04 VM that has 2x 2GHz cores + 1024MB of RAM. The HDD is passed through to it as a USB device passthrough.

I made a shared folder on both drives (so 2 in total) and shared them by SMB with my Windows 10 laptop, where I mounted the shares as two network drives.

When I first started to copy (large) files from share1 to share2, it did it with a solid and stable 110MB/s. As expected. Of course this dropped to 5-6MB/s when doing thousands of very small files. But now that the HDD is about 60-70% full and I've started to transfer large files again(movies, 5-40GB per file), I only see 45-55MB/S most of the time. With some periods of 80ish MB/s. Neither CPU nor RAM is maxed out. And it did 110MB/s before using the same setup. Anyone and idea why I lost my speed and it sometimes returns to full speed?

It must be noted I specifically picked this drive because it uses CMR and not SMR. I have already made that grave mistake (and corrected it now with the WD20PURZ CMR). The old drive is also CMR.

Thanks in advance!

EDIT:

While I've been typing this and making the screen shots, the speed has dropped even lower to 35-45MB/s. CPU load has also dropped accordingly.

EDIT2:

Later on, the speed picks up slowly again, as can be seen in the third screenshot I just added.

Zitat von raulfg3

For me, it is a capacity problem of the USB3 port that cannot give the speed that the network asks for, you should do tests that allow you to conclude if it is that or not.

I would have guessed that if that was the bottleneck, it wouldn't have worked before @ full 110MB/s speed.

And according to my calculation, 5Gbps (625 MB/s) should be more than enough to read and write at 110MB/s simultaneously, and then some, right? Or am I forgetting some kind of (large) overhead?

I've searched the forum for similar problems. I'll try again since I guess your hinting the answer to my question is already written somewhere over here.

I left all the drive settings at default for now. So APM disabled and write cache off. This way, I got a solid 110MB/s straight out the box.

I do remember from when I setup my first drive, the write cache on setting made the write speed go up from 40ish to 80MB/s (2.5" 2TB CMR USB HDD). But since this drive seemed to get its advertised speed without the write cache, I thought it was best to leave off, decreasing the chance of filesystem corruption. I'll give it a try with write cache on to see what happens.