I created my pool using 9.3 about a week ago and now after an update I'm getting this warning message. In the past this action would have to be done to obtain extra features for your pool but this warning seems to let a person think that this is mandatory. I'd like to know what is going on. I don't want to file a bug report unless I know what is going on. If this action isn't required for compatibility issues then it should list the limitations or features based on upgrading the pool.
The reason for the warning is that we have actually observed, in the field, serious issues with the following very specific combination:
- User has a pre-9.2 pool (usually 9.0.x) and 9.3 kernel.
- User is doing a lot of CIFS sharing and uses extended attributes
- User is manipulating a lot of files (we're not sure if directory creation/deletion is involved, or what) while extended attributes are also in use
This, after a certain period of time, results in pool corruption.
We have tried like crazy to replicate this and have been entirely unsuccessful, which is why it is a warning and we're not posting long messages to the forum going "ZOMG! You MUST upgrade your pool or you will DIE!" We don't know that for sure, and we have existing customers with "old pool, new OS" that are doing just fine. It's a real mystery, but one thing we can say for sure is that we have never observed this when the pool version was > 28. So, for now it's just a warning. You can not heed it and suffer no problems whatsoever, or you can not heed it and die a messy death. We have no idea which side of the coin you will land on or how to predict it. If we did, we'd find this and fix it once and for all. :( We've asked the experts too, and they're stumped.