Expected write speeds

[ziggy99]

I got an Unraid server with 3 WD Red SOHO NAS 4TB hard drives as data disks and 1 WD Red Plus NAS 8 TB as parity disk.

 

The hw specs of the server is quite good with an Intel I7-8700 and 32 GB RAM.

 

If I test writing a large file to the server (e.g. > 5 GB), the initial speed is good. I can see that it it utilizing almost the full 1 gbps network speed, but after apprx. 2 GB of data written, the speed falls to half of that. 350-450 mpbs of network utilization. The same if I write smaller files - the initial writing is fast (> 100 MB/s), but after some time it falls to 50 MB/s.

 

Should I not expect any better speed than this from these hard drives? Why is the initial speed good, but then it decreases?

It does not seem to be related to network speed - because it does not utilize the full speed of the link.

[itimpi]

If you are writing directly to the array then the speed is constrained by the overheads of updating the parity disk as explained here in the online documentation accessible via the ‘Manual’ link at the bottom of the GUI or the DOCS link at the top of each forum page. The Unraid OS->Manual section in particular covers most features of the current Unraid release.

[polishprocessors]

FWIW I'm seeing 50-100MB/s write speeds to my 14TB parity, 8-14TB drive array.