In VSVM, any snapshot volume can be writable.No matter how many iterative operations have been produced in generating a snapshot volume, another snapshot based on it can still be created.

• 该快照机制针对于普通应用，允许快照逻辑卷正常读写，支持对任意快照逻辑卷（可能是经过多次快照迭代操作产生的逻辑卷）继续创建快照。