A Month with Apple's Fusion Drive
by Anand Lal Shimpi on January 18, 2013 9:30 AM EST- Posted in
- Storage
- Mac
- SSDs
- Apple
- SSD Caching
- Fusion Drive
Final Words
For the first time since late 2008, I went back to using a machine where a hard drive was a part of my primary storage - and I didn’t hate it. Apple’s Fusion Drive is probably the best hybrid SSD/HDD solution I’ve ever used, and it didn’t take rocket science to get here. All it took was combining a good SSD controller (Samsung’s PM830), with a large amount of NAND (128GB) and some very aggressive/intelligent software (Apple’s Core Storage LVM). Fusion Drive may not be fundamentally new, but it’s certainly the right way to do hybrid storage if you’re going to do it.
It seems that Fusion Drive is really made for the user who doesn't necessarily have a ton of applications/data, but does have a reasonable sized media collection. For that user, Fusion Drive should be a reasonable approximation of a well managed SSD/HDD setup with your big media files going to the HDD and everything that you launch frequently living on the SSD. I’m always going to ask for a larger cache, but I do believe that 128GB is a good size for most client workloads and usage models today. For me in particular I’d probably need a 256GB cache for Fusion Drive to win me over, but I understand that I’m not necessarily the target market here.
The real question is whether or not it’s worth it. I’m personally a much bigger fan of going all solid state and manually segmenting your large media files onto HDD arrays, but perhaps that’s me being set in my ways (or just me being right, not sure which one). Fusion Drive doesn’t do anything to mitigate the likelihood that a hard drive will likely fail sooner than a good SSD, whereas if you go with an internal SSD and external (Thunderbolt or USB 3.0) HDD RAID array you can control your destiny a bit better. Unfortunately, in situations where Fusion Drive is a choice, you don’t often have that flexibility.
On the iMac, Apple limits your options quite a bit. You can either buy a hard drive or the Fusion Drive on the 21.5-inch model, there’s no standalone SSD option. There the choice is a no-brainer. If you’re not going to buy your own SSD and replace the internal HDD with it (or try to see if OWC’s rMBP SSD fits), then the Fusion Drive is absolutely right choice. You’re paying handsomely for the right ($250 for 128GB of NAND is very 2011), but if you’re not willing to crack open the iMac case this is really the only way to go.
For the 27-inch iMac the decision is similarly difficult. Apple does offer a standalone SSD option, but it’s for a 768GB model that will set you back $1300. All of the sudden that $250 Fusion Drive upgrade sounds a lot more reasonable.
On the Mac mini side the decision is far simpler. The Fusion Drive is only available on the $799 configuration (for $250) but so is a 256GB SSD upgrade for $300. As long as you’re ok with using an external hard drive for mass storage, here I’d go for the big standalone SSD. The usual caveat applies: this is only true if you’re not interested in cracking open the mini yourself and using a 3rd party SSD.
To make things simpler, I made bold the options I'd choose given Apple's current lineup in the table below. Note that this is still assuming you're not going down the DIY route (if you do go down that path, buy the biggest SSD you can find and rely on some external mass storage for everything else):
| Fusion Drive Options | |||
| Mac mini (2012) | 21.5-inch iMac (2012) | 27-inch iMac (2012) | |
| Base System Cost | $799 | $1299/$1499 | $1799/$1999 |
| 1TB Fusion Drive | +$250 | +$250 | +$250 |
| 3TB Fusion Drive | - | - | +$400 |
| Largest Standalone SSD |
256GB (+$300) |
- |
768GB (+$1300) |
I am curious to see how long of a roadmap Fusion Drive has ahead of it. Will NAND get cheap/large enough that even the iMac can move to it exclusively? Or will we end up with systems that have more than enough NAND to easily store everything but large media files for even the most demanding of power users? In less than a year Apple could double the size of the NAND used in Fusion Drive at no real change to cost. I suspect another doubling beyond that would be necessary to really make Fusion Drive a one size fits all, but then we're talking ~2 years out at this point and I don't know how static everyone's usage models will remain over that period of time. Go out even further in time, to the post-NAND era and there are some really revolutionary things that can happen to the memory hierarchy altogether...
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Richard Fairbanks - Saturday, January 19, 2013 - link
Thanks, Anand, for yet another timely article!I do almost all my work in code (i.e. text) with few graphics. I want to ensure reliability in case of disk failure.
Thus I am considering getting a 2012 Mac mini, opening it up, and adding a 256GB Samsung 840 Pro, in addition to the default 1TB HDD. (The 256GB capacity would allow me a 25+% spare area.) This is my ideal configuration for many reasons.
If I partition the HDD to match the 256GB SSD (leaving ~750MB for random, non-critical data), is it possible to create a RAID 1 array between the SSD and the 256GB HDD partition? (Full backups are made daily.)
In theory, this would allow all the array reads to come from the SSD for fastest response, and still maintain a mirrored HDD that could be booted from should the SSD fail. (If only the HDD partition could be a ZEVO ZFS format! ;-) )
Thoughts? Thanks!!
NCM - Saturday, January 19, 2013 - link
Richard asks: "If I partition the HDD to match the 256GB SSD (leaving ~750MB for random, non-critical data), is it possible to create a RAID 1 array between the SSD and the 256GB HDD partition?"That's an interesting question. I think the problem would be that there is no "master" disk in a RAID 1 array. Each slice is treated equally. You're hoping that read/write activity would be first served by the faster SSD, with the HD slice catching up in the background on its own time. I don't know that there's any evidence it would work like that, or, putting it another way, that anyone has written a RAID controller to make it happen that way.
It would be interesting to try it out.
We have some Mac Pro towers that I've set up SSD boot/application drives, but we rely on conventional Time Machine backups to an internal HD rather than a RAID mirror.
name99 - Saturday, January 19, 2013 - link
It is possible to create a RAID 1 in the way you are thinking using AppleRAID.What you want to do is simple enough that you can do it in DIsk Utility using the GUI.
If you really insist on going hardcore, hit Terminal and look at diskutil.
And you can boot off such an AppleRAID system.
HOWEVER I suspect you will be very unhappy with the results. A system like that can deliver snappy reads (because they'll mostly come from the SSD) but writes will be gated by the HD, and the system will frequently feel an HD system.
It is ALSO possible that you won't even get the read speeds you imagine.
When I used AppleRAID in this way (mirroring two HDs) a few years ago, it seemed to me that reads were also slower, and my assumption was that the system, assuming you cared primarily about data correctness (that's why you were mirroring rather than striping), performed both reads and compared the results before passing them up to the file system. Which suggests that your reads will ALSO be gated by the HD performance.
I'm also not sure what problem you believe you are solving with this. SSD failures are simply not that common. You can protect against them using Time Machine. If you REALLY are scared, you can have Time Machine alternate between two (or more) different backup drives.
It seems like a huge amount of pain to solve a problem that barely exists and that can be protected against much better in other ways.
name99 - Saturday, January 19, 2013 - link
To add to what I said, the AppleRAID mirroring stuff DOES work in terms of reliability, in that if one disk dies, you can just pop it out, replace it, and have the other disk copy to it. But, as I said, you pay a substantial hit in performance for this privilege.cjb110 - Saturday, January 19, 2013 - link
Gaming would have been an interesting 'use' case for the Fusion. When your playing you obviously want the fast access of SSD, but unless its your favourite game, it might not get used much and moved to the HDD.Also Games being much larger 'applications' would quickly fill the SSD if the Fusion just had a simple 'If App = On SSD" rule.
klaudyuxxx - Saturday, January 19, 2013 - link
They reinvented the wheel. 128 GB flash + 1-3TB HDD fused into a single volume?! AKA HYBRID SAMSUNG HARD DRIVESNCM - Saturday, January 19, 2013 - link
You really haven't bothered to read the article, have you? Or perhaps it's a reading comprehension issue.nerd1 - Saturday, January 19, 2013 - link
Typical apple - charging $$$$ for non-tech-savy people.It's way better to have a proper SSD (most laptops and desktops now have mSATA port) in terms of both performance and cost. Yes, I know that swapping the HDD of any apple device kills the warranty and most apple customers don't know how to upgrade a single component.....
Andhaka - Monday, January 21, 2013 - link
Nope, swapping the HDD with a SSD does not kill the warranty and many Apple users do that (I have done it on a 4 years old Macbook).But if other people find it better to pay for the Fusion solution (and a good solutions it seems to be) good for them.
Cheers
pichemanu - Saturday, January 19, 2013 - link
Hi Anand,i saw that in order to test a "pure ssd" setup you connected a 830 ssd to the imac over USB 3. As far as i know the best transfer rate over USB 3 is around 250 MB/s and the worst is well... terrible.
Considering the best case scenario for the iMac:
-USB 3 connected SSD would do 250 MB/s
-SATA 3 connected SSD would do 322 MB/s (taken from your article)
The performance would be 6.94 for fusion drive and 10.19 for a "pure SSD". This is an increase from 114% advantage for the "pure SSD" to 147% advantage for the "pure SSD".
If on the other hand your USB connected SSD did not write at max and a SATA 3 connected SSD would (that is 350 for the samsung 830 on an intel Z77 SATA 3 port) that difference would skyrocket.
Did you check that on your particular workload the USB 3 connection was not a bottleneck?
Thank you.