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I have an early 2009 Mac Pro(4,1). Firmware upgraded to a '10(5,1), 24GB RAM, upgraded processors to two quad core 3.46 GHz Xeons', NVIDIA GeForce GTX 760 2GB. I'm looking at the next upgrade options and an SSD comes to mind. As you probably know, the '09 and '10 have SATA II, not III. What I want to know is the performance gain from a HDD to a SSD running at SATA II, as opposed to III, worth the upgrade? Can SATA II SSDs be found at a lower price than SATA III drives, if they can be found at all?

I know I can either get a SATA III card or a PCI SSD and not have the performance hit, but that adds enough to the cost of the upgrade to not fit in the budget at this time.

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Empirically, the answer is 'Yes'.

I have a very similar machine - 4,1 -> 5,1, dual 3.46GHZ Xeons, 64GB RAM & also an older 3,1.

Both now have an SATA III 840 EVO 1TB as boot drive [best available at the time of purchase] in the first optical drive bay [leaving room for your usual 4 HDs in the regular bays. Adapter bracket a few quid/dollars/shekels from eBay.
On the 4,1 it connects directly to the cabling in the bay, the 3,1 needs a longer SATA cable down into the main body, under the cooling fans, where the two 'secret' SATA ports are.

No, they don't run at SATA III speeds, but boy do they make the entire machine more responsive. Boot time down from a couple of minutes to 15 seconds. iTunes [the slowest to launch that I know of] now launches in about 5 seconds. Finder is zippy & responsive, no more waiting for it to fill a window.

You get so used to the speed you don't notice it until you have to use a machine with a spinning HD again.

Speed test - SSD

Speed test - HD

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Yes it’s worth the upgrade. Even over a SATA II bus, the performance boost will be immediately noticeable with a SSD:

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From Is A SATA 3Gb/s Platform Still Worth Upgrading With An SSD?:

"The real key is getting an SSD into your machine. Just have a look at what happens when our 840 Pro goes up against the fastest desktop hard drive we've ever benchmarked, Western Digital's ValociRaptor. The disk didn't stand a chance in any of our synthetic or real-world tests."

I’d also recommend purchasing a SATA III SSD as they are backwards compatible. You’ll find a much wider selection at pretty much the same price point (in some cases, cheaper). Additionally, you’ll be able to use it in your next machine ;)

  • I am not sure what "Average I/O operations" are. There is a chart, shown later in the reference you posed, comparing sequential transfers in MB/s. The results shown in this chart more closely match the technical specifications given by the manufactures of both drives. The chart demonstrates how a SATA II (3 Gb/s) interface can limit the preformance of a SSD. – David Anderson Sep 7 '16 at 8:15
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    @DavidAnderson, the chart is measuring the number of I/O operations that can happen per second, i.e. randomized fetches from random parts of the disk. With a HDD, the drive head needs to seek to the right track and wait for the right location of the disk to rotate under the head to access requested data. Subsequent blocks might be on different tracks and thus the head needs to keep thrashing around. This is typical of database read/write patterns. Given that SSDs have no moving part that needs to seek data, performance is instantaneous as shown. SATA II/III makes little difference here. – bjb Sep 7 '16 at 16:45
  • @bjb: SATA refers to the transfer of data to/from the drive and the host (computer). In this case SATA II is transfers at 3 Gb/s and SATA III transfers at 6 Gb/s. Your comment compares the internal workings of HDDs verses SSDs. So am I to infer that you are saying the following? Even though the latency of a SSD is far less than a HDD, both SSD and HDD have large enough latencies that a 3 Gb/s transfer speed adds little to the overall transfer times of data when access randomly. – David Anderson Sep 7 '16 at 18:04
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    @DavidAnderson: correct, SATA refers to the transfer of data and II vs III refers to bandwidth (3Gb vs 6Gb). Your comment questioned the chart above which doesn't refer to the SATA speed, but rather how quickly a SSD sends requested data back to the OS; HDDs have at least two mechanical activities before it can return data VS an SSD which does not. In some respects it is the more important measure for the original question since HDDs rarely saturate SATA bandwidth because they can't get to the data fast enough. SSDs CAN saturate because of this and thus why the industry is moving to M.2, etc. – bjb Sep 8 '16 at 12:16
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The performance gain with an SSD comes from the zero seek latency/time, all data is instantly accessible. That's where an SSD in consumer computers is beneficial. Massive IOPS or extreme bandwidth and NAND speeds won't help a user that much, but has a real impact in server applications and large data transfers (i.e. to and from RAM).

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You seem to have answered your own question. If a SATA III card is available but not in the budget, you might as well get SATA III SSD now and add the card later.

SATA II data transfers over the connecting cable occur at a faster rate than the internal speed of a HDD. SATA II cable transfers are slower than the internal speed of a SSD. This is why SATA III created.

HDDs internally have a transfer rate of about 200 MB/s, where as SSDs have an internal transfer rate of over 400 MB/s. When a SSD uses a SATA II interface, the actual transfer rate is limited to 300 MB/s. When using a SATA III interface, a SSD is not limited by the interface itself. Therefore, there is about a 50% performance improvement when a SDD replaces a HDD using a SATA II connection. But, to truly see an improvement, you will need to SATA III connection.

Drive manufactures now offer drives that include both SSD and HDD components. Externally, the drives appear as single devices, but internally cache frequently used data in the SSD. This can give SSD performance at HDD prices. These drives are often referred to as Solid State Hybrid Drives (SSHD).

Apple offer their own version of SSHD technology. These drives are referred to as Fusion Drives. The difference is that OS X is aware the the Fusion Drive is actually a HDD and SSD paired together. When a Fusion Drive is installed, you have to use Core Storage when partitioning the drives.

  • "There is a slight performance improvement when a SDD replaces a HDD using a SATA II connection. But, to truly see an improvement, you will need to SATA III connection.” ??? that’s just patently false. – njboot Sep 7 '16 at 6:47

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