How to create a new partition on FileVault disk on MacOS I have a 500GB disk on MacOS encrypted with FileVault 2.

I have successfully resized the disk to 250GB.

Now I want to create another partition to install another MacOS on the 250GB free-space of the disk.

But DiskUtility failed on me, it just can't create the new partition I wanted and showed me no error at all.

How could I safely create the new partition I need?

This the result printed out from the command $ sudo gpt -r show disk0

          start       size  index  contents
              0          1         PMBR
              1          1         Pri GPT header
              2         32         Pri GPT table
             34          6         
             40     409600      1  GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B
         409640  488940896      2  GPT part - 53746F72-6167-11AA-AA11-00306543ECAC
      489350536    1269760      3  GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC
      490620296  486484731         
      977105027         32         Sec GPT table
      977105059          1         Sec GPT header
Your 500 GB disk has about 250 GB of unallocated disk space (starting at block 490620296 and ending at block 977105026).

To create a new partition in the unallocated disk space you have to boot to another boot disk.

Preparation:


Attach a backup drive and backup your drive.
Detach the backup drive
Restart to Internet Recovery Mode by pressing alt cmd R at startup. 

The prerequisites are the latest firmware update installed, either ethernet or WLAN (WPA/WPA2) and a router with DHCP activated.
On a 50 Mbps-line it takes about 4 min (presenting a small animated globe) to boot into a recovery netboot image which usually is loaded from an Apple/Akamai server.

I recommend ethernet because it's more reliable. If you are restricted to WIFI and the boot process fails, just restart your Mac until you succeed booting.

Alternatively you may start from a bootable installer thumb drive (preferably Yosemite or El Capitan) or a thumb drive containing a full system (preferably Yosemite or El Capitan). If you boot to a full system and login as admin you have to prepend sudo to execute some commands like gpt ... or newfs_hfs ...!


Modify the GUID partition table and add a new partition


Enter diskutil list and gpt -r show /dev/diskX (with diskX: the disk identifier of your internal disk (probably disk0)) to get an overview. In the commands below I assume the disk identifier is disk0.
Now add a new partition with: 

gpt add -b StartBlock -i IndexNumber -s size -t type disk #size has to be dividable through 8!


In your case:

diskutil umountDisk /dev/disk2 #unmount the FileVault2 volume if unlocked
diskutil umountDisk /dev/disk0
gpt add -b 490620296 -i 4 -s 486484728 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk0

Get the disk identifier of the new partition

diskutil list #probably disk0s4

Format the new partition:

newfs_hfs -v "Volume Name" -J /dev/disk0s4

To quit Terminal enter:

exit


and quit Terminal
Open Disk Utility to verify the new volume
Reboot


In case you want to move the recovery partition to the end of the disk first

This is not recommended if your first main volume is encrypted with FileVault2. The first Recovery HD contains some encryption keys to unlock the FileVault2 volume. Moving/changing the Recovery HD may render your FileVault2 volume unaccessible and useless.


Create a new recovery partition and clone the old one:

diskutil umountDisk /dev/disk2 #unmount the FileVault2 volume if unlocked
diskutil umountDisk /dev/disk0
gpt add -b 975835264 -i 4 -s 1269760 -t 426F6F74-0000-11AA-AA11-00306543ECAC /dev/disk0
dd if=/dev/disk0s3 of=/dev/disk0s4

remove the old recovery partition and add a new normal partition

diskutil umountDisk /dev/disk0
gpt remove -i 3 /dev/disk0
gpt add -b 489350536 -i 3 -s 486484728 -t 48465300-0000-11AA-AA11-00306543ECAC /dev/disk0

Get the disk identifier of the new partition

diskutil list #probably disk0s3

Format the new partition:

newfs_hfs -v "Volume Name" -J /dev/disk0s3

To quit Terminal enter:

exit

Open Disk Utility to verify the new volume
Reboot