MySQL read-write Master with many read-only Slaves over shared storage?
NO.  Do not attempt to have a single copy of the data with multiple copies of mysqld accessing it.  I don't know if that ever worked; if it did, I suspect it has atrophied over the years as changes have been made.

Think about it...  Each copy of the server has lots of stuff cached in RAM.  To coordinate that with other servers would require writing things to disk; this defeats the performance goal.  When a write occurs; all traces of it would need to be immediately flushed to disk, and all the other servers would need to know to read it and replace whatever is cached in their RAMs.

With FusionIO, check to see that you can safely turn off innodb_doublewrite.

How many queries/second?  Do you have any 'slow' queries?  (That is, there are other ways to beef up performance, than just hardware.)