OmniOS/ZFS/Windows 7: "Save as" from within applications lags 5 seconds for all file sizes over CIFS/SMB

Solution:

The problem only affects OmniOS r151018, not previous versions. This thread on the omnios-discuss mailing list was exactly about my problem, quote from Geoff:

I saw a similar thread with Nexenta forum. There seems to be an issue with opslock. I disabled opslock and we are good now.

svccfg -s network/smb/server setprop smbd/oplock_enable=false

Not sure why this isn't biting more people.

So, biteCount++; I guess. The problem was solved by applying the fix and doing a fast reboot.

Lessons for the future: before attempting any troubleshooting, just use the advanced search on the official mailing lists, because most likely your problem already occurred on someone else's machine. Also, spin up a quick VM to rule out any software, updates or configuration errors before looking for hardware errors.

How I got there:

After several different tests as seen in the updated question, I narrowed it down to either software problems or hardware/driver conflicts on the specific hardware. To rule out the second, I installed two fresh OmniOS virtual machines, r151018 and r151016 on another host and configured by hand a basic SMB share on each of them.

The r151018 experienced the problem, r151016 works fine. I suspect I did not notice it in my very first tests, because I only rolled back some updates on r151018, not back to an earlier release. I think the problem must have been existed longer than I assumed.

When looking for a way to only update packages one by one, I looked at the mailing list and searched for smb from the last 6 months, where the correct solution/same problem popped up, dated back from May.