I'm running into a little bit of a snag on a high log send queue in a 2014 SP1 Asynchronous Mode AlwaysOn Environment with a secondary replica in Azure.
For one of our higher transaction volume DB, we are seeing log send queue sizes up to nearly 2GB for extended periods. Initially we saw a CPU bottleneck on the secondary due to the sizing of the Azure VM, which we corrected. However we were still left with some high log queue sizes and slow send rates, coupled with respective high re-dos.
We traced this back to an issue with IO using the following error log message: "There have been 112313856 misaligned log IOs which required falling back to synchronous IO. The current IO is on file..." More specifically this has to do with unmatched disk sector sizes between our SAN and Azure LUNs.
This knowledge base article seems to address exactly what my issue is: https://support.microsoft.com/en-us/kb/2936603
However its a year old and applies to CU5, which is about a year old, and we are about 8 patches past CU5. Additionally I can't find any official documentation from MS on trace flag 1800. Does anybody have an similar experience with either this error message, or information on trace flag 1800? If so was your issue corrected with this flag, or were you forced to match your LUN disk sector sizes between both replicas?