Comment 2 for bug 1209199

Hi Xiaoxi,

So I was not aiming to solve the auto_flatten issue here, but rather to support it as a future. As you say, many copies of a snapshot will likely cause a performance degradation and this was my understanding for the need to auto-flatten under certain circumstances. We do, however, need to consider the tradeoff between volume creation time/impact and performance. This modification will allow the user to optionally have copies performed using copy-on-write up to a certain number of copies. Therefore, the user will be able to

either (a) disable copy-on-write and have full copy for each volume
or (b) allow a fixed number of copy-on-write clones before switching to full copy (not flatten)
or (c) allow infinite copy-on-write

Then, if/when we decide best approach for auto-flatten we can add it in.