Comment 1 for bug 1209199

Copying in message from Chen, Xiaoxi:

"I have discussed with josh about the auto-flatten feature, almost share the same idea with you from code basis but go to different direction.
My proposal for auto-flatten is when there are too many children, then when user want to delete the parent volume, we don’t actuall flatten all children ,instead, we just lazy-delete the parent volume instead --- to prevent a flatten storm.
Your proposal is if a snapshot has too many children ,then disabled the CoW mechanism,this is another approach for prevent a flatten storm, but it’s doubtful for performance reason, for example ,if you have a snapshot of OS-DISK, and a lot of volumes cloned from that snapshot, it’s likely the base-image(to be exactly, the snapshot) will be very hot and thus be cached in DRAM. So it may be even faster than you do a full copy."