Having an issue with new Mirotik CRS226-24G-2S+in and SFP+ (S+85DLC03D)
Connection via 5 meter mm fiber cable to a broadcom 57710 card (W2012R2 server)

Link is OK initially, pushing 900+megabits/sec bidirectionally measures with iperf from a 1Gb/sec connected test system. after a while (days?), performance drops to nearly zero in one direction (iperf said .02 gigabits/sec)
To fix it, all I had to do was pull the fiber patch cable out of the CRS, and plug it back in.
Not much experience with 10G or with fiber. Any troubleshooting tips?
I am thinking the regular stuff like -replace fiber patch cable with spare, replace NIC and transceiver in the server with spare, -swap around the SFP+s in Mikrotik. I have no spare SFP+, but I can see if the problem follows the SFP+, or stays with the Slot/Cable/Server.
-other SFP+ goes to an ESXi host, so I can't run iperf natively on there, but I will add VM to the W2012R2 server testing next round. When everything is working well I get 8.9-9.5 gb/sec both ways between those two.
-check logs in Mikrotik for transmission errors. I checked the interfaces section in Winbox, but no errors at all were logged there. Where else can I check?
-check logs in esxi and windows server for transmission errors.

any other Hints?

Well it took a few days, and the problem came back.
The symptom is the same. performance to a windows server connected to the SFP+ , slot 2 starts off just fine, but after a few days in one direction (FROM the server to the switch) drops like a store, about 2% of what it should be. To fix it, all you have to do it unplug the fiber for few seconds, then plug is back in. The first time I replaced the fiber, that didn't help. This time I swapped the 2 SFP+ transceivers.

any hints on how I can troubleshoot this?

I have the exact same CRS226 switch & S+85DLC03D SFP+ transceiver connected at 10Gbps to my CCR1009 SFP+ (same transceiver) without issue.

Perhaps the problem is with your server end ?

Or incompatibility between the CRS226 and the Broadcom card ?

You may want to clean your fiber ends. Its extremely easy to smudge the end and cause issues. Also I believe the Mikrotik SFP slots support DDM to measure light levels and such if the SFP supports this.

I replaced the cable, and one SFP+ (Microtik) now, so that would leave the optics in the Server NIC side transceiver. Since the problem is temporarily "fixed" by removing and re-seating the fiber connection on the microtik side, I didn't think that likely to be a problem. If/when the problem returns, I will replace the server NIC side transceiver with a spare. thanks!

This type of cleaner is great for cleaning the optic side of things. It can also clean the fiber end as well.

http://csmedia.corning.com/opcomm//Reso ... TA_AEN.pdf

swapping the SFP+ between the two seems to have fixed it. maybe dust/dirt???