Why a Fusion Drive si better than a 256Gb SSD (personal opinion)

[yjchua95]

Just my thoughts...Spinners have no future in modern high end desktops....just one thing I was wondering about: why is the internal SSD so much faster than the external TB SATA SSD(700 MB/s read vs 380MB/s)? The SSD in the 5K iMac is no NVMe but also SATA as the external. The Thunderbolt interface should be linked relatively close to the PCIe bus.....

SATA3 is limited to 600 MB/s at most (taking 8b/10b overhead into account).

The internal SSDs in the retina iMac (along with every other Haswell Macs) don't have NVMe, but they're at least PCIe. Because of the fact that they're connected over PCIe, they're not capped by the limits of SATA3, even though they're using the same MLC NAND flash found in more expensive SATA3 SSDs.

Meanwhile, if you stick a PCIe drive via Thunderbolt, you'd get about 700MB/s as well. However, if you stick a SATA3 drive (e.g. Samsung 850 Pro) via Thunderbolt, you'll be limited to SATA3 speeds and also more overhead due to it being an external connection.

So basically, if you connect a SATA3 SSD over Thunderbolt, the speeds are limited by the hard drive's SATA interface, not the Thunderbolt port.

 

[sevoman]

No it won't, SSDs are faster better then a combined SSD/hard drive combination.

When data is off loaded to the hard drive, access speeds will decrease.

I don't think its rocket surgery, to see how a single digital solution, is superior to a merged digital/mechanical solution. If I have no need for 1TB of storage, there's no need to get a fusion drive. The SSD will be better.

Pure SSD is not only faster for all tasks than a fusion drive, but also with a fusion drive you still have a mechanical hard disk drive that the ssd portion requires to work. If either fails the other wont work. SSD has far greater reliability than a mechanical drive. Just ask yourself: how many times has the SSD in your cell phone failed and had to be replaced? being used constantly pretty much nonstop reading and writing for years. avoiding anything mechanical with moving parts is the way to go.

 

[nobodykeys]

Slightly old thread but I thought I'd share my experience of Fusion Drives.

So I set one up myself using a 256SSD + 750GB HDD, both internal. I used the Mac OS command line commands to join them into a Fusion drive, and ran this for over a year. No question, this was faster than the HDD on its own.

However, I suffered a SSD failure after a year, and around the same time, the HDD also failed. I don't know for certain why they failed together, but it did seem a bit of a coincidence considering they were running as a Fusion Drive. Either way, I also realised that even had only 1 failed, I would have had to restore everything from backups for the complete Fusion Drive.

Since replacing the drives, I've ended up leaving the SSD and HDD separate, no Fusion, and doing some manual set up so that I have the OS, Apps, and other caches that require high speed access, all on the SSD, and the HDD then houses most of my user folder (except stuff that needs to be on the SSD for performance reasons), and any other stuff. This also allows me to have a separate boot partition on the SSD for a small Mac OS install dedicated specifically for using my laptop in a live music performance setting where speed, reliability, is key.

I can confidently say that the separate SSD + HDD solution is far better than the Fusion Drive. Examples are:-

• Adobe Lightroom much faster (RAW cache is set to be on the SSD, original media sits on the HDD)
• iMovie editing much faster (I store my main projects on the HDD, and move whichever project I'm working on, into an SSD library whilst I work on it, and then move it back to the HDD when I'm done)
• General responsiveness much quicker (as it would be for a Fusion Drive)

The key thing is, after using the Fusion Drive for a while, I wasn't convinced it really was doing all the moving around of commonly used files as all the marketing suggests, and as has already been discussed above, there were some things less used but that needed fast access if I did use them. Indeed, after I did some research, I found evidence of the fact in reality, the Fusion Drive in the long term does indeed not live up to its promises and instead, is used as a temporary cache for writing to the Drive (not reading).

By the way, all this is on a 2008 Macbook Pro, so not exactly a fast machine either - but it is pretty decent with this set up.

I'm convinced that Fusion Drives are the stop gap for end users who really do not want to do anything other than just plug in and go, whereas if you're willing to be a little more active in your File Management (and there are tons of guides online), you can get a lot more out of a separate SSD + HDD set up. When I upgrade to a new iMac, I'm gong to get an internal SSD, plus an external HDD via the Thunderbolt interface.