I have a Mac with OS X 10.10.5 on a HD which had 4 partitions.
Using Disk Utility I deleted one of the 4, intending to slightly grow the 3rd (containing the OS), leaving space for a new partition to install El Capitan.
This has been my practice up to now when a new version comes out.
I booted to another HD and deleted the partition, but it then proceeded to resize the 3rd partition YoodenVranx to use all the free space.
There seems to be no way to change the Partition Layout, or resize the partition.
I rebooted and used diskutil to list the current state.
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Fenchurch 80.0 GB disk0s2
3: Apple_HFS BxxxxxData 70.0 GB disk0s3
4: Apple_CoreStorage 349.0 GB disk0s4
5: Apple_Boot Recovery HD 650.0 MB disk0s5
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: Apple_HFS YoodenVranx *348.6 GB disk1
Logical Volume on disk0s4
Best Answer
To get some additional un-allocated disk space on disk0 to create a new partition you have to shrink your CoreStorage Volume Group and all subsequent CoreStorage items.
To resize the CoreStorage Volume Group in your case you have to use the Terminal booted to an external boot drive.
Preparation:
Boot from your external drive or a bootable installer thumb drive (Mavericks or Yosemite)/a thumb drive containing a full system (Mavericks or Yosemite).
or
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 to 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.
Modify CoreStorage stack:
First you should get an overview of your disks and the partition layout:
Enter
diskutil list
:Example listing:
with disk0: your internal disk, disk1: a fictional external boot drive with 100 GB containing your boot volume (BlinkenDonx) and disk2: your CoreStorage Volume Group YoodenVranx residing in disk0s4.
Enter
diskutil cs list
Example listing:
Now resize the CoreStorage volume with
with LVUUID: UUID of the logical volume and size: the final size of your CoreStorage volume.
Examples:
to shrink it to 300 GB
to shrink it to 295.4 GB
Your Recovery HD should be moved automatically.
To add an additional partition for your future El Capitan volume enter first:
to get an overview
Example listing:
with i=1: EFI 2: Fenchurch 3: BxxxxxData 4: Apple_CoreStorage 5: Recovery HD and about 70.2 GB free space (assuming you shrunk your CoreSorage volume to ~279 GB in the previous step to be able to create a new 70 GB volume).
To create a new volume with
gpt
you have to unmount all mounted volumes on disk0 (first the CoreStorage volume, which has its own disk identifier disk2 but resides on disk0, then all other mounted volumes on disk0)Now add a new JHFS+ volume with gpt:
StartBlock is the number of the first block in the unallocated space and NumberOfBlocks is the number of free blocks or smaller. NumberOfBlocks has to be dividable through 8!
For the example above that's:
exit
and quit Terminal.