Write caching will definitely speed up MySQL performance, but only do that if you have a BBU (battery backup unit). I've encountered several debates about read caching and MySQL performance. You should test MySQL with both read caching on and off to see which works out better for you.
Write caching does significantly improve performance since the data being written to the disk is first written to the RAM on the RAID controller. The RAID controller then writes the cached data to disk later, but for the application, the disk write is complete and it's off to other things.
A BBU is used to keep data in RAID controller RAM from being lost in the event of a power failure. Without a BBU, this data would be lost when the power goes off and that can cause file system corruption. For databases, the lost data could be enough to make the database unreadable.
Without a BBU, you need to use write-thur for the RAID controller. This means that the write operation is not complete until the data is written to the disk, but it's much slower. But this ensures no data loss should the power go out.