Here is how you can repair the disk, if following error in Disk Utility is seen after running Verify Disk on a SSD.
Error Message
Volume bitmap needs minor repair for under-allocation
Invalid volume free block count
Steps to repair disk
Startup in single-user mode, by first shutting down. Then push the power button and immedietly press and hold Command+S till you see the terminal screen. (Related Apple Support Information)
In the terminal run /sbin/fsck -fy multiple times till a “disk appears to be OK” message is shown.
Then run reboot command to restart OSX. After the Mac has restarted, run verify disk again to verify that the disk has been repaired.