OS X El Capitan Fusion Drive - any reason to be concerned?

Not sure if anyone but @Lee_Ars has experience on this…

Mid-2012 MBP, 500GB spinning platters for the current (only) drive. I’ve got a shiny new Samsung EVO 850 500GB SSD that I want to mount in it (with an OWC Data Doubler). I’ve got about 95GB free on my current drive.

Originally was going to do a clean OS install on the SSD, use Migration Assistant to bring everything over, reformat the platters, then put my photos & other bulk media on it. Then I remembered Fusion Drive and started thinking about doing FD to make one 1TB volume and let Core Storage handle it all. Clean install, use MA from my Time Machine drive, and I’m all set.

Now I’m being told that SSDs “don’t like being filled to capacity” - and FD will (mostly) fill the SSD to capacity and then start pushing cold data to the platter and keep the warm stuff on the SSD.

Is this really a concern? Can/should I enable TRIM on the SSD while in an FD configuration? Any good recommendations for the best way to set all this up?

I’m not really sure. I bought the 120 gig version of that drive for my hackintosh project, though. :slight_smile:

I thought Fusion Drives had to be specific HW from Apple or it wouldn’t engage. Do you need to use some sort of trick to get it registered? I’d be hesitant about ‘forcing’ an SSD and HDD into a configuration in which data might be lost, but I may be paranoid.

Everything I’ve read (which, admittedly, isn’t much beyond @Lee_Ars’s articles and things he’s linked to in them) seems to indicate that it’ll work with any drives. I’ve even heard (don’t recall where) that on El Cap, if you start a clean install w/ 2 drives in the system, it’ll offer to set up Fusion for you.

I could be completely wrong though.

I think you can combine drives to make Fusion Drives, indeed there are weird SD card gimmicks that promise to do all that… over the blazing USB2.0 speeds of the SD card bus -.-

I have the exact same SSD in my 2011 MacBook Pro, and I have the old 750GB spinning disk hooked up to the router in a caddy as a Time Machine drive. Unless you’re coming close to capacity, I’d say just do your first plan and start afresh like I did.

Oh, and enjoy your new über-nippy Mac :wink: seriously the boost in speed and general performance (in my case, swap performance, because I really should upgrade to 16GiB when my game’s mod files are pushing the application to 7-8GiB >.>) is worth every penny.

I’m tentatively planning for my Hackintosh to have 3+ SSDs as dedicated boot drives for various operating systems. (Keep the data on the home NAS whenever possible.)

I haven’t done any testing in the past couple of years, but iirc it’ll work with any set of drives. If you’ve read the pieces I wrote, then you know about as much as I do! I know Anandtech did some additional testing, but not a whole lot.


Whoever told you SSDs “don’t like being filled to capacity” is guilty of gross oversimplification—there’s a lot in that statement to unpack. The super-short version is that SSDs can be more performant when they have lots of free space, but most SSDs are over-provisioned—that “240GB” SSD contains 256 or more GB of NAND, so even when it’s full, it still has spare pages to use for garbage collection. Depending on how far along the SSD is in its lifespan, it might need to do more garbage collection operations to keep enough pages free to handle your workload…or it might not. There’s no way to really tell, but honestly, if you’re buying a new SSD, it really doesn’t matter. SSD lifespan and performance issues are pretty much solved problems.

With respect to TRIM: Taken on its own, you should always enable TRIM if you have the option because there’s essentially no downside. However, I have no idea if you should enable TRIM on your Fusion Drive-attached SSD, or if OS X will even allow you to do it, since it’s treated as a component of the main core storage volume. Now that ElCap lets you enable TRIM for non-Apple SSDs, you could always try and see!

Well, I didn’t do the Fusion Drive. But not for the reasons you might think.

After doing a full TM backup (and then manually forcing it a half-dozen times because I’m paranoid), I cracked the machine open, set to work, and…stripped the head of a screw I have to remove to gain access to the optical drive. It’s not a system-critical screw, but I’ll have to get after it w/ a Dremel drill bit to drill the screw out.

I did a direct swap of the HDD instead. Popped the SSD in, booted from my installer USB stick, and waited. And waited. And waited some more. Restoring from the TM backup took eight hours (drive is in a FW400 enclosure). When it was all over:

  • My drive had 20GB more free space than the HDD did
  • My Dock was somewhat screwed-with
  • My open Safari tabs weren’t kept
  • Dropbox had to re-authenticate
  • Google Drive had to be told where its folder is, and re-authenticate
  • CrashPlan appeared to have freaked out, but I think it sorted everything out and didn’t have to re-upload all of my stuff.

The computer is a lot zippier.

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