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I'm running 10.9.5 on an iMac, where I have two hard drives (SSD + HDD) and Superdrive installed. The way the disks are mounted is not conventional:

/dev/disk0s2 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
/dev/disk1s2 on /Users (hfs, local, journaled)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)

disk0s2 is internal SSD drive and disk1s2 is internal 1TB HDD drive.

I've read that upgrading to Yosemite will convert my drives to fusion drive1, though I have not found detailed information what would happen in my situation. I have a couple of questions:

  1. did anybody try upgrading Mavericks to Yosemite with similar drive configuration? What were the results?
  2. will Yosemite convert my two drives to Fusion drive? (I read that in order to convert it, it needs to erase contents, so I'm assuming that upgrade procedure won't create fusion drive)
  3. if the fusion drive will be created automatically, I guess I can't control which data is on SSD and which data is on HDD anymore, right? I use virtual machines heavily (vmware) and I don't want them all on ssd...

Since this machine is my primary workhorse, I'm reluctant to just try and see if it works. I've upgraded my Macbook air (single ssd drive) without issues, fwiw.

  • Yosemite converts HFS+ volumes into Logical Volumes in a Core Storage Volume Group, but I don't think it automatically creates Fusion Drives. (In most cases.) But I'm not totally sure about that. – alexwlchan Oct 28 '14 at 17:04
  • interesting question ;-) 1. no i didn't but i would revert the mappings 2. dunno but usually the conversion is non-destructive blog.fosketts.net/2012/10/03/mac-os-corestorage-convert, additionally it should be revertible. 3. Just build a 2nd partition for the vms (or whatever you want to store on the hdd). it won't benefit from the ssd and by implication the vms will reside solely on the hdd. – klanomath Oct 28 '14 at 17:06
  • @klanomath: creating a separate partition on HDD is an interesting propostion. Reverting the mappings not so much - there isn't enough spaceon ssd unfortunately. I guess I'll just have to have some faith :). I'll report my findings. – miha Oct 28 '14 at 20:39
  • @miha don't you have a backup? – klanomath Oct 28 '14 at 21:00
  • @klanomath: of course I do. I have three separate backups. Even so, it is best if you don't have to restore :) – miha Oct 29 '14 at 6:37
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The answer is: OS X did not upgrade my disks to Fusion Drive (or CoreStorage).

[miha:~]diskutil cs list
No CoreStorage logical volume groups found

Probably because of the unconvetional layout. Or perhaps some other unknown reason.

  • dancing on the razor's edge... i tried to find a solution (force the installer to keep the old partition layout) for 1 but couldn't find anything... – klanomath Oct 28 '14 at 21:58

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