skew

https://blog.hindsight.it/index.php?/archives/14-Demystifiying-ACp...html
ACp introduces the concept of the skew value.. essentially a threshold, counted in number of write operations. Below the skew value, the device pairing operates in async mode, and above the threshold it switches to synchonous mode (the skew value normally defaults to 65536 operations).


https://community.emc.com/message/387388

Newer versions of Enginuity no longer support Semi sync. So I'll just discuss ACP and Sync mode.

Leaving skew for later, the easiest method to manage this is just to set the mode you want to operate in.

If you want to run in ACP_DISK, use "symrdf -g xx set mode acp_disk".
If you want to run in Sync mode, use "symrdf -g xx set mode sync"

If the write workload is high enough that you never catch up in acp mode (and this is your primary concern), you can manually set the mode to sync. Since setting the mode to sync will have impact on your host write response times, I personally think it may be better for you to do this manually. However, you can use the "skew" value and it will toggle into and out of sync mode all by itself.

Now to try to be specific to your questions..
Q1) If you are still running code that has the choice of sync or semi-sync and you plan on using the skew value, then yes- I would first set one of these modes to establish which "primary" mode will be reverted to when you exceed the skew value.

Q2) It kinda sounds the same as Q1 - so again, if you are going to set skew value, do this to set the primary mode.

Q3) The primary mode is considered Sync or Semi-Sync. The adaptive copy is considered secondary mode. The statement is true whether or not you set a skew value. It's just that by not setting the skew value, the Symmetrix will not automatically transition back to the Primary mode. So, you are correct - just picking on terminology

Q4) I would use the skew if you have some reason to run in ACP mode and have decided that you don't want do build up invalid tracks beyond some predetermined limit (the value you would set for skew) - and - it is acceptable to your application to run in sync mode whenever you get to that value.