>My questions are:
>1 - If one of the GFS slaves RAC1 or RAC2 is down, will be the other slave server able to access to the shared file system /u04?
If the slave server was shutdown cleanly, the other slave server will be able to access the shared file system. However, if the slave was fenced off and was not rebooted the locks it holds will not be released. In that case the other slave server may not be able to access all files on /u04. If you have ilo or rilo in your HP servers you can use remote ilo fencing agent.
>2 - If the master is down, will be the both GFS slave servers able to access to the shared file system /u04 simultaneously?
No. The slave servers will not be able to access the shared file system if the master is down!
this is my two cents knowledge... experts please add to this!!