MySQL InnoDB over a Raw Device in an Active/Passive topology
It's worth noting that InnoDB's write ahead log (WAL), the ib_logfile*, is not the only thing that will need a file system. You have:


System tables in the mysql schema that likely use the MyISAM storage engine (.frm, .MYD, .MYI per table) (most are now using InnoDB in 5.7)
.frm files for each InnoDB table, even when using the shared system tablespace (table metadata that's required)
MySQL log files (error log, general log, binary log)
SSL artifacts 
auto.cnf (where the MySQL instance UUID is generated and automatically stored)
db.opt file for each schema (in /&lt;datadir&gt;/&lt;schema&gt;/)
.par file if you create a partitioned table (gone in 5.7)
.trn and .trg files if you create triggers 
InnoDB tmp tablespace (5.6+)
Persisted buffer pool page map (ib_buffer_pool, 5.6+)


All of the above are typically within the data directory, so as long as you have datadir=/some/valid/fs/path -- that's also replicated (e.g. DRBD) or shared (e.g. NFS, GFS, OCFS) between the two nodes -- then you'll be fine. 

It's worth noting that the .frm, .par, .trn, .trg, and .opt files will go away with the new Data Dictionary.

Stay tuned for some big announcements there in the coming months! :)  

It's not clear to me why you're using the RAW device? I'm sure you have your reasons though. :) 

Good luck!