http://blog.csdn.net/do2jiang/article/details/5136921
我终于知道答案了，这几天在参加iSCSI Enterprise Target的开发组的讨论 ， 这个能从理论上解释：
iSCSI really is just the handling of data blocks to and from the hard disk. Think of it as an extension of the hard disk that goes across the wire.
If you have multiple servers connected to a volume it is exactly like having a shared SCSI bus between multiple hosts. There is nothing in the SCSI controllers to prevent you from corrupting your shared volumes. This kind of control needs to come from the operating system. The OS needs to know the volume is shared and either a special file-system or special handling needs to take place. I don't know of a shared file-system in Windows, but Microsoft Cluster Services allow one server at a time access to a shared volume using SCSI Reserve/Release.
iSCSI must follow the SCSI protocol and the only function available to aid in shared access is SCSI RESERVE/RELEASE, which is a form of mutex.
-Ross
这样的话 ， SCSI本身不能解决互斥的问题， 必须由kernel来解决。
通过google ， 知道 iSCSI本身不能作share storage ， 必须配合cluster file system才能实现真正的simultaneously read and write to and from a same target device .
GFS 就是这样一个文件系统 ，由RedHat开发， 而且是open source的。