Q: how to clean-install Mavericks to a fusion drive?
Because I cannot find a complete answer here or anywhere else, I seek information about reinstalling Mavericks on a 1TB fusion drive on my late 2013 iMac. I see discussions about reinstalling, backing up data, Boot Camp issues, rebuilding a fusion drive, making a fusion drive from scratch, and the like; but I do not find the level of detail I am seeking about starting over with a fusion drive. I upgraded to Mavericks from Mtn Lion and now see hints that I needed to do something special to take advantage of the properties of this drive.
That said, here are my questions:
(1) When I "Command-R" reboot to Recovery and get to the Disk Utility, I see a separate 1TB HD as an extended partition as well as a 125GB drive that is root (/), which I presume is the SSD. To accomplish the clean installation, do I format BOTH? Or will formatting only the 1TB HD suffice? Does formatting only the 1TB HD also take care of formatting the SSD? Maybe it's not advisable to format the SSD ...?
(2) Does the downloaded Mavericks installer loaded onto a USB stick using DiskMakerX have the capability to do this clean install properly? or is it necessary, in order to take advantage of the fusion drive properties (SSD+HD), to download Mavericks Installer after wiping the HD so that support for the fusion drive is maintained?
(3) Because I am curious, where does OS X (I mean the OS, not data) reside after the installation is done? on the SSD? on the HD? I ask this because I have read that "the OS remains on the SSD," but, seemingly in conflict, that the SSD is for quick access to frequently used programs and data. Both could be correct.
Sorry for the length of this. And thanks.
iMac (21.5-inch, Late 2013)
Posted on Feb 19, 2014 8:13 AM
Post a screen shot of the Disk utility window when you are booted to OS X not the Recovery HD.
A Fusion drive should should up in all disk utility windows, no matter where or how you are booting the system, as a Logical Storage Volume, as one drive, not as two independent disks.
Open Terminal and type diskutil list and copy the text output and post it.
It is unclear to me whether your iMac is actually booting into OS X at this time?
Your original questions.'
1) you shouldn't see 2 independent drives. You should see one drive and it should be listed as a Logic storage volume.
2) If you downloaded Mavericks on that iMac using the and then made the install USB drive from that download then it should work on that iMac. But you might first have to reinstall Mt Lion from the Online Internet Recovery system as all new Mac's come with a special built of OS X designed specifically for the specific Mac it is being installed on. That special built contains the proper drive package for the newer hardware in newer Mac's. The Mavericks download you got from the Mac App Store may or may not include those special, new, drivers for the newer hardware. I'm unsure on that point.
3) Since a Fusion drive appears as one disk to OS X the files for OS X could be anywhere on either physical disk. The fusion drive system tries to fill up the SSD first so in the beginning most if not all data, OS X or whatever, will be placed on the SSD. Over time the FDS will move some data off the SSD as it sees fit. So OS files that aren't used often or at all might at some point be moved from the SSD to the rotating HDD. This is all done without any notice to the user.
A Fusion drive system will not be as fast as some other Mac with only a SSD installed, no Fusion drive. On a FDS any data could be placed anywhere across both drives or placed on one or the other. That is totally up to the FDS, not the user.
The process to do what you want is straight forward, even in that OWC article, Boot from the Recovery HD and download OS X and install it. That is once the Fusion drive has been created.
At this time it is unclear, at least to me, whether your Fusion drive is really setup correctly. Posting a screen shot of a Disk Utility window when you are booted into OS X, not the recovery hd, should tell us that. But as far as I know if the Fusion drive is setup correctly it should always appear as a Logical Storage Volume. That is where 2 physical disks appear as one large volume. Not as 2 independent disks.
Posted on Feb 21, 2014 3:31 AM

