Anyone know what Apple DELETED the RAID option from Disk Utility in El Capitan ...... I know the option is still there but you have to use Terminal to access it. At least in Yosemite setting up a RAID is still in DISK UTILITY !!!
Your guess is as good as mine why Apple removed RAID, maybe they thought it isn't used by significant % of users and therefore they don't have to support it?
I wish Apple would seriously improve 10.11 Disk Utility, it has far too many bugs at the moment.
Mavericks will be getting security updates till 10.12 comes out, so you'll probably get security patches until October 2016, then you're on your own.
I personally had a huge number of issues with Mavericks, and wouldn't ever go back to it. Have you tried a clean install of El Cap?
I clean installed El Capitan both on iMac and Mac Pro. While it was faster than Yosemite didn't see any other clear improvements. At the moment it has too many bugs for me to consider using it, I probably test it again on the iMac once Apple releases last 10.11 version.
I am not worried about the lack of security updates, I used Snow Leopard several years after it received no more updates without any problems.