Can I Simply Add an HDD to an Existing SSD Boot Drive?

[rayward]

I have just completed a project to upgrade the innards of my mid-2010 iMac with a new HDD and a new SSD. The OS is now installed on the SSD, but I want to make this a fusion drive with the HDD. When I try to follow the Terminal instructions to create one drive, it cannot unmount the SSD (presumably as this is running OS X).

Can I simply add the HDD to the same volume on the SSD, or do I have to go through the pain of booting from an external drive?

Thanks!

 

[simonsi]

You would have to boot from an external, create the fusion drive, that would format both SSD and HDD and then you would need to reinstall everything to the fusion.

TBH there wont be any real world benefits of the fusion over you deciding to keep OS and apps on the SSD and data on the HDD. What the fusion will mean is more complications and potential problems (as you have just discovered), as it treats both drives as a single volume so any failures will mean you have serious problems.

My advice would be to run them as seperate drives.

 

[satchmo]

Thanks, but I'm not looking at creating a Fusion drive. Just two separate drives. I just want the OS and apps on the SSD and use the HD for data storage.
The question is more about physical location and being able to boot from the SSD sitting in the caddy.

 

[rayward]

Thanks, but I'm not looking at creating a Fusion drive. Just two separate drives. I just want the OS and apps on the SSD and use the HD for data storage.
The question is more about physical location and being able to boot from the SSD sitting in the caddy.

My SSD is "mounted" to the back wall of my iMac with sticky pads (included in the kit from OWC), under the optical drive and attached to the 3rd SATA port on the logic board (that last part is not as easy as it sounds as the 3rd port is on the backside of the logic board and a bugger to get to). If you are keeping your old HDD, you can boot to that and then format the SSD, install the OS on it, make it your boot drive and move over what files you need. If both are new drives, you'll need a external boot source, like a bootable thumb drive (pretty easily done - I used option 2). If you're keeping the original HDD for storage only, you'll probably want to backup your data, reformat it and put the data only back on that drive to keep it clean.

In my case, both my drives were new, but that didn't matter as I wanted to fuse them anyway. I booted the Mac from a thumb drive and created the fusion drive with a few simple steps through Terminal. After that, I simply re-installed my system from a Time Machine backup to the new fusion drive. I prefer the fusion approach as it means not having to worry about file management; I just let the OS handle all that in the background.

 

[satchmo]

@rayward, thank you very much for the links and help.

 

[simonsi]

Thanks, but I'm not looking at creating a Fusion drive. Just two separate drives. I just want the OS and apps on the SSD and use the HD for data storage.
The question is more about physical location and being able to boot from the SSD sitting in the caddy.

I have just completed a project to upgrade the innards of my mid-2010 iMac with a new HDD and a new SSD. The OS is now installed on the SSD, but I want to make this a fusion drive with the HDD. When I try to follow the Terminal instructions to create one drive, it cannot unmount the SSD (presumably as this is running OS X).

Can I simply add the HDD to the same volume on the SSD, or do I have to go through the pain of booting from an external drive?

Thanks!

Bizarre, I only have 5 posts showing here, I reply to the OP #1 and satchmo refers to a different question???

Anyhow. OP, no you can't add an HDD to a Fusion volume in that way, the volume needs to be created in DU, then formatted as a single volume, then OS/Data loaded onto it as you wish, any existing data on the existing SSD volume will be lost.

 

[simonsi]

I prefer the fusion approach as it means not having to worry about file management; I just let the OS handle all that in the background.

Yep, the downside is the single volume is susceptible to issues on either underlying SSD or HDD so you may get more issues and have to restore the entire Fusion volume if required for an issue that would only affect either SSD or HDD if unfused. I just runthe OS and Apps from my SSD and have data and a backup bootable partition on my HDD...