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New Fusion Drive

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storage_fusion.jpeg

For those confused about the new Fusion Drive, I wrote something up about how I think it will work.

Apple’s new Fusion Disk technology sounds amazing. It combines fast Flash or SSD storage with the more space abundant HDD but there is some confusion on how this will work. Many people are comparing it to hybrid SSD drives that have been available for some time that basically cache a small amount (less than 8GB) of data to the SSD part of the drive. That means it keeps 2 copies of data that it thinks you are going to use for faster access. The small amount of size means that not much can be cached and it would constantly be copying and deleting the files onto the SSD and as benchmarks have proven, not really give you a performance boost. The new Fusion Disk is going to work completely different.

During the presentation, Apple showed the insides of the new iMac that clearly point out a full size 3.5″ HDD and on the left side the Flash memory. The Flash may be a card like what is used in the MacBook Air and MacBook Pro w/ Retina or soldered on. Phil Schiller I think mistakenly said that both the flash and the HDD were part of the same part but they are clearly separate from the layout.

In Mac OS X 10.7 Lion, CoreStorage was added as a new way for Mac OS to handle the storage systems. Most people are not using CoreStorage unless you are using FileVault 2 in Lion or OS X 10.8 Mountain Lion. The way it works is CoreStorage actually creates a virtual disk on top of the physical disk and then presents it to the operating system. I have FileVault turned on on multiple disks and using the command diskutil cs list in the terminal you can see how it looks.

CoreStorage took some physical space from the actual hard drive and created a Logical Volume Group. Inside that group you have physical volumes. Right now, this is just a single physical volume. Under the LVG you have the Logical Volume Family and finally the Logical Volume, the thing you actually see in the finder as your HDD.

What the Fusion Drive process is going to do is create a LVG with both the Flash Memory and the HDD and combine them into a single Logical Volume that you will see in the Finder. Behind the scenes, CoreStorage will automatically place any system files on the Flash storage along with your most used files for faster access. Anything else will be stored on the physical HDD storage without you needing to know what files are where. But, rest assured, when you go to your Documents or Pictures folder, it will be there just like you left it.

http://threedevices.com/2012/10/24/how-the-fusion-drive-on-the-new-imac-and-mac-mini-will-work/
 
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Interesting thing about this technology is, that alle read commands are performed on SSD first. The OS later then decides to swap a file to the mechanical drive, when used rarely. Vice versa, the FusionDrive swaps back files from the mechanical drive to SSD, if used more often. TimeMachine will do a backup of both drives as one drive, so you can reconfigure a Mac from this source.

Sources:
http://www.macobserver.com/tmo/article/digging-into-fusion-drive-details
http://www.engadget.com/2012/10/23/apple-fusion-drive/
 
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Thats what I believe will happen. And all system files /system, /library, /dev, etc will all stay on the SSD.
 
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so do you think we could use this fusion drive with a ssd and hdd in our builds !? Is it just software so I ll also be able to use this with a macbook pro ssd and hdd in a caddy ?
 
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I am trying to locate the special Disk Utility app right now to see whats up and if we can get this to work. I will try to inject the app into the 10.8.2 unibeast and see if we can make it work. Worst case I will boot off another 10.8.2 erase my SSD and HDD and then using the 10.8.2 installer and see if it works.

Mark
 
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Thanks for testing !
(I'll pray on my side to see a good result :thumbup:)
 
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Well I am at work but really wanted to get this tested and working. So I decided to play around with CoreStorage. I was using the help of this site.
http://blog.fosketts.net/2011/08/05/undocumented-corestorage-commands/

Anyway he mentioned in this article that he was unable to get a multi disk LVM created. I was able to with 10.8.2. I created an LVM using a 32GB flash drive and a 9TB external FW drive I have here. Disk Utility sees it as a LVM and I even have the same limitations as Fusion Drive with only being able to create one additional partition. Going to reboot and Install an OS to the LVM and just see what happens. It won't really test the logic side to see if its just builtin because well its a USB thumbdrive and a FW800 device. I will test some more with a spare SSD and a spare HDD I have when I get home too.

Mark
 
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Just realized what will probably be our biggest issue as I'm doing this test at work with a real Mac. Chimera will have to be written to be aware of the lvm. I have zero clue what that entails but this is probably going to be the biggest hurdle on the hackintosh
 
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