Apple announced Fusion Drive last week, a hybrid storage system combining a 128 SSD with a 1TB or 3TB spinning HDD into a single volume.
According to Apple, Fusion Drive will be available in November and will allow users to reap the benefits of an SSD while enjoying the storage capacity of a traditional hard disk drive. This technology comes as a new storage option for the company's latest iMac, and will be done automatically by Mac OS X.
Mac OS X will place the core system and other frequently used applications and files on the SSD to automatically manage the combined volume for faster access. At the same time, it will keep lower-priority applications and data on the standard hard drive.
When the company announced its new Fusion Drive hybrid storage solution along with the refreshed iMac earlier this month, many were left wondering whether existing hybrid drives would also work with current Macs not configured with Apple SSD and HDD combo.
In a post to Tumblr, developer Patrick Stein has now unofficially confirmed that Mountain Lion provides Fusion Drive support for current Macs. The developer detailed how he managed to "build" a hybrid device compatible with Apple's new hybrid storage technology.
Stein used the Terminal version of disk utility to setup a SSD and a separate HDD so that OS X recognized both as a single logical volume, i.e. what Fusion Drive basically promises to do. To combine an SSD and HDD into a single volume, Stein's working solution involved an SATA-connected 128GB SSD and USB-attached HDD.
To build a single logical volume Stein used Core Storage, the OS X feature linking two separate storage units into one volume group, thus combining the SSD and HDD. Next, the developer created a 466GB HFS+ volume, more commonly known as Mac OS Extended, to allow for easy file creation and transfer.
"Now in DiskUtility the individual disks no longer show, but the Logical Volume (LV) shows as one disk," wrote Stein. "Part one is finished, we've created a single Volume consisting of a SSD and a HDD."
Stein further created several directories with files amounting to 140GB of data by using the "mkdir" and "mkfile" commands to test whether the rigged setup worked as a Fusion Drive. The process involved funneling data to the SSD until the 120GB mark, after which the remaining files were written to the HDD directories 11-13.
To force reads located on the HDD, the developer used the "dd" command. Fusion Drive reads data located on the HDD to determine which files are frequently accessed and should be relocated to the faster SSD. To monitor whether any files were transferred to the SSD, Stein used "iostat" after stopping the read process.
The system reportedly began dumping data from the SSD to the HDD immediately after the "dd" process, and stopped after roughly 14GB of copying. When Stein first tried to readout data from directories 11 to 13, he found they were still located on the HDD. After an hour of reads, however, Stein found the files were being accessed from the SSD, meaning Fusion Drive had successfully transferred the data.
Stein's informal test proves that Fusion Drive is active and usable on older Macs as well. In follow-up posts on Tumblr, Stein later detailed further explorations into the workings of Fusion Drive, noting that he managed to use both ZFS and the default HFS+ file system for OS X with it. The developer performed all his tests with a standard installation of OS X 10.8.2.
On the other hand, while Stein proved it can be done, configuring the hybrid storage devices is no easy task. It is uncertain for now whether Apple will provide Mac owners with an easy solution to configure their own components without having to run Terminal and use line code commands.
