Contribute
Register

Understanding and Using Fusion Drive

SJ_UnderWater

Moderator
Joined
Dec 3, 2010
Messages
707
Motherboard
Gigabyte GA-H55M-S2V
CPU
Intel i3-530
Graphics
HIS HD 6570
Mac
iMac
Classic Mac
Mobile Phone
Android
There has been a great deal of misinformation about Fusion Drive recently, and this thread aims to dispel any rumors.

What is Fusion Drive?
Fusion Drive is Apple's marketing name for a Core Storage feature that automatically tiers commonly-used files (really file blocks) between solid state (flash) and rotational (hard disk) drives. A Logical Volume Group in Mountain Lion created with an SSD and HD will automatically exhibit the behavior Apple is calling Fusion Drive, thanks to JollyJinx's work
Fusion Drive, being block-based, must be built at install-time and will wipe the contents of the drives used to create it. There is additional difficulty when repairing. While the special copy of Disk Utility included with Late 2012 Mac desktops is the only version capable of operating on a Fusion Drive, it may still require a drive wipe in the case of corruption, and must be repaired from the Installer. Fusion Drive is not a backup solution, and may in fact be more susceptible to filesystem corruption; exercise caution. Once created, a Fusion Drive can only support one additional partition, a Windows or Linux installation, for instance.
Finally, Chimera/Chameleon is not yet capable of booting Core Storage volumes, like Fusion Drive or FileVault2, you must use Clover EFI

What is Core Storage?
Core Storage is a Logical Volume Manager for OS X which abstracts certain filesystem, partition, and drive concepts, and goes a long way towards modernizing the increasingly-old HFS+ filesystem, enabling features such as full disk encryption. When using Core Storage, the system will contain one or more Logical Volume Groups, which "import" or contain physical drives, raid sets, or images. These Physical Volumes combine to form the disk space which will be used in one or more "exported" Logical Volume Families, which provide the Core Storage features such as FileVault2 and Fusion Drive. The Logical Volume Families in turn "export" one or more Logical Volumes which behave like partitions. Logical Volumes are formatted with a filesystem such as HFS+.
At the moment, Core Storage volumes can only be created with the `diskutil` command line (Terminal.app) utility. FileVault2 is an exception because the volume created maintains a one-to-one relationship with the physical disk, and the encryption can be applied "live" and in the background.

How do I create a Fusion Drive?
Fusion Drives must be created at install time, and will wipe the existing contents of the drives used to create it.
  1. Boot your Installer USB, and launch Terminal
  2. Run
    Code:
    diskutil list
  3. Note the disk numbers of the SSD and HD (like disk0, disk1, disk2)
  4. Replace <SSD> with the SSD disk number, and the same for <HD>. You may also replace "Fusion Drive" with a different name. Run
    Code:
    diskutil corestorage create "Fusion Drive" <SSD> <HD>
  5. Run
    Code:
    diskutil corestorage list
  6. Note the UUID of the Logical Volume Group, like DE85044F-EADA-4F26-93B7-8CD0ADF006EC
  7. Replace <UUID> with the UUID you noted above. You may also replace "Macintosh HD" with a different name. Run
    Code:
    diskutil corestorage createVolume <UUID> jhfs+ "Macintosh HD"  100%
Your Logical Volume is now complete, formatted as HFS+J, and ready for installation
 
Joined
May 22, 2011
Messages
901
Motherboard
GigaByte Z390 M Gaming
CPU
i9-9900K
Graphics
RX 560
Mac
iMac, MacBook Pro
Mobile Phone
iOS
Can I make with 2TB HDD with 120GB SSD?
 

SJ_UnderWater

Moderator
Joined
Dec 3, 2010
Messages
707
Motherboard
Gigabyte GA-H55M-S2V
CPU
Intel i3-530
Graphics
HIS HD 6570
Mac
iMac
Classic Mac
Mobile Phone
Android
a new post in the forums has reported success booting Fusion Drive with Chimera, with the addition of "rd=uuid uuid=<lvuuid>" to Kernel Flags in org.chameleon.boot.plist, where <lvuuid> is the UUID of the final Logical Volume, but this requires manually installing the bootloader components to both drives. I haven't tested this method yet, but a script might improve the success rate.
 
Joined
Aug 21, 2011
Messages
214
Motherboard
ASRock Z77E-ITX
CPU
i5 3570K
Graphics
GTX 650
Can you only fusion ONE SSD and ONE HDD? I currently have ML running on a 128GB SSD where I also keep my apps, and two 1TB HDD in raid 0 for storage. Can I fusion the SSD and the raid 0 pair? I imagine if this were possible, I'll get benefits of both fusion *and* raid 0. True?
 

SJ_UnderWater

Moderator
Joined
Dec 3, 2010
Messages
707
Motherboard
Gigabyte GA-H55M-S2V
CPU
Intel i3-530
Graphics
HIS HD 6570
Mac
iMac
Classic Mac
Mobile Phone
Android
as far as I can tell, no one has tried more than two drives, but based on what is known about Fusion Drive it probably won't benefit. The free space on the SSD is treated as the "landing zone" and kept >4GB, so that drive will accept all new writes until full and unable to migrate. While it would be theoretically possible to stripe any additional SSD and HDs, that isn't how FD is expected to work, and I wouldn't recommend it anyway for the possibility of failure. Remember that the speed increase with FD is dependent not only on the SSD's size, but also its write speed.
 
Joined
Oct 23, 2013
Messages
16
Motherboard
Lenovo T540p
CPU
i7-4700MQ, 20BFS27X00
Graphics
Intel HD 4600, Nvidia GT 730M, 1920x1080
Mac
Classic Mac
Mobile Phone
Finally, Chimera/Chameleon is not yet capable of booting Core Storage volumes, like Fusion Drive or FileVault2, you must use Clover EFI

What about using the latest Chimera/Chameleon - is there Fusion Drive support yet?
 
Joined
Dec 27, 2015
Messages
1
Mac
Classic Mac
Mobile Phone
how do you split them back up? Is it even possible? I searched the internet and found nothing on the subject.
 
Top