Re: What a waste
Write cache - yes. It is definitely turned off by most RAID controllers.
Read cache AFAIK usually is not.
Frankly, 64M vs 16M is not likely to make a hell lot of difference in most production deployments. It will make a difference only if you have a clued up sysadmin who have optimised the layout by hand or if you have spent a hefty wad of cash on a system that does that for you. That is the minority of sites. The majority will just stick the lot in a driver array and format it which means that metadata (journals, indexes, allocation tables) and data will end up on the same disk (courtesy of flat RAID5/6). As a result any data access to a single disk will always be accompanied by some metadata access which together will thrash the cache out to the point where it is useless.