As you know, the OS X partition Recovery is quite important with many available features such as password reset, ternimal, repair disk, reinstall OS X … However, by some reasons, It is gone when holding the Option key and even not available in Startup Disk.
No Recovery Disk in Startup Disk
HOW TO RESTORE YOSEMITE RECOVERY PARTITION?
Step 1: Firstly, use the following command line to make sure Recovery HD exists.
Step 2: Enter the following command line to show all CoreStorage of Logical Volume
Sudo diskutil cs list
This command will show all results in order: Group(LVGs)–> member (PVs)—> exported volumes(LVs).
You have to copy the Logical Volume UUID at member LVs.
Step 3: Enter the following command line.
diskutil coreStorage revert LVs_UUID
Step 4: Restart the Mac and hold the Option key to see the result.