Strange SMB Behavior (Caching and Dumping?)


macrumors newbie
Original poster
May 4, 2012
Hello everyone!

I know the SMB implementation on Mac OS is notoriously bad, however I'm noticing something strange about my file server and I'd like to know if anyone might be able to offer some insight.

I have a Mac Mini running as a file server for my small video production business with TBs of external hard drives connected and shared using USB 3.0.

Prior to Catalina, I was using AFP as my file sharing protocol, but I ran into a number of problems with AFP after upgrading to Catalina and decided to switch to SMB.

However, using SMB, I'm noticing that files transferred TO my server FROM my iMac connected via gigabit ethernet appear to be "cached" and then "dumped" onto the storage destination in chunks. I don't know exactly how to describe it other than that.

If I initiate a transfer from my iMac to my server and then watch my network traffic and the disk activity on my server, I can see that files are transferred to the server at roughly the maximum my gigabit ethernet connection can allow, which is 117.19 MB/s. During this time, there is no disk activity occurring on the destination disk on my server. This will go on for roughly 10-20 seconds, and then all network activity on the transfer will stop. Then, for the next 10ish seconds, I will see significant writing activity on the destination disk. This cycle continues for the duration of the transfer.

However, if I go to the server and initiate the transfer from there, grabbing the files off my iMac across the network onto the server, this "caching" behavior does not occur. Similarly, if I grab files via the iMac FROM the server TO the iMac, this caching behavior does not occur.

When I was using AFP, this caching behavior never occurred.

So, in summary, my SMB transfer speeds are satisfactory when network activity is occurring, but then it seems to pause in 10-20 second increments in order to actually write the data to the destination disk.

Is this normal behavior? Can anyone offer any insight into what's happening or a solution?

Thank you!
Last edited:


macrumors 68030
Feb 15, 2008
Nope - guess I've stumped the forum!
Try this -

I was hitting caching and dumping issues that were exacerbated by a not-so-great replacement SSD the previous owner had put in the mac mini. Last night my mm server had a kernel panic (twice) while i was trying to transfer files to it.

I now no longer see a read/write process on my SSD when i'm checking in on it with istat menus - just writing directly to the shared HD. Still some unexplained and random-length pauses where the HD is presumably catching up... but an order of magnitude better than before over my gigabit ethernet.