RAID 1 write performance

[imreloadin]

I've noticed that over the past couple of times that I've transferred large (13 totaling ~5GB) sets of files over to my NAS (HDDs are two 4TB HGST 0S03664's) that the write performance seems to be kind of odd as indicated in the screenshot below:

 

As you can see it drops down rather severely several times over the duration of the file transfer, even as low as 0 bytes/s as indicated in my screenshot. The peak transfer is 111 MB/s which is where it levels off at the top which is indicative of the drives being two 7200rpm drives. I guess I'm just not sure if this is normal behavior and I just haven't been paying attention at this point or if this indicates some kind of problem. I just checked the SMART metrics on them and both drives seem to be healthy.

[Mira Yurizaki]

The drop off may be due to file system overhead and the latency it takes for the NAS to say it's fine to write again.