Ever since the first beta of Sierra (Mac OS 10.12), I have been interested in Apple’s new file system, APFS. As the first new file system released by Apple in almost 30 years, I knew this file system would be built from the ground up using the best techniques for providing speed, reliability and features found in modern file systems. (For more on APFS, click here).
As soon as I could I was able to create an APFS volume on top of a SoftRAID volume, I started testing APFS for speed. I wanted to see if it was faster than the HFS Extended volumes I had been using for decades. I also wanted to test APFS with different RAID levels on both SSDs and HDDs. Would Apple’s promise that APFS was a “low latency” file system translate to faster reading and writing? Did APFS deliver faster speed on the HDDs, which are used throughout the film and video industry?
For all my early testing, I used AJA System Test with files of differing sizes. AJA system test writes a single large file to a volume and reads it back to determine how fast the volume reads and writes file data. Results are displayed in a speed/time graph, which shows how much read/write speeds vary during the test. This makes it easy to see if the file system has to pause every so often to take care of housekeeping chores, leading to slower performance.
While some of the early releases of APFS resulted in volumes, which were slower than HFS Extended on the same hardware, it soon became clear that APFS was improving. After a few months, new versions of APFS gave the same results with AJA System Test as HFS Extended.
I always want to stress test software as much as possible—the faster the storage device the harder it is for the OS to keep up with. So what better way to do this than by using two of OWC’s upcoming ThunderBlades with a 2017 MacBook Pro? Each of these soon-to-be-released devices incorporates 4 SSD blades; using two of them to create an 8-blade stripe, I could get performance way faster than possible even with a single Thunderbolt 3 port.
So just how fast is the release version of APFS which comes with High Sierra? Can it keep up with HFS? To find out, I created an APFS volume using a beta copy of SoftRAID version 6 and two ThunderBlades.
I repeated the AJA System Test using a large variety of disks and RAID levels (created with SoftRAID). The speeds of APFS and HFS Extended volumes were always within a few percentage points of each other regardless of the type of disks or RAID level I was using.
So far, so good… However, after High Sierra shipped, I decided to dig into the performance of APFS even further. I had really only tested speeds with a single file operation; how would APFS perform with a more likely scenario—copying numerous files between volumes? To my surprise, I found that copying a large number of files from one APFS volume to another (on a second disk of the same type) was always slower than performing the same operation with HFS Extended volumes. The speed difference was most pronounced with HDDs—where APFS could take almost twice as long to copy—but also existed on SSDs, and even ThunderBlades.
I needed to thoroughly test the comparative speeds of APFS and HFS. So I created two source volumes, one APFS, one HFS Extended, both with High Sierra (macOS 10.13) installed. I also created two target volumes, again one APFS, one HFS Extended, on separate disks. I then used the Finder to copy four startup volume folders (Applications, System, Library and Users) from the APFS source volume to the APFS target volume. I repeated the test, this time copying the same four folders from the HFS source volume to the HFS target volume. Copying these four folders involves copying over 160,000 files, which total just over 12 GB in size. The Finder copying was timed using a stopwatch.
This test was performed several times using a 2017 15” MacBook Pro as the source, and either ThunderBlades, 10TB Hitachi SATA HDDs (connected over Thunderbolt) or a 960 GB OWC Extreme Pro SSDs (also connected over Thunderbolt) as the various targets. In the graph below (showing the results) you can see that each APFS volume takes longer to copy files than an HFS Extended volume on the same hardware. Copying files between two APFS volumes, each on separate HDDs, takes almost twice as long as using HFS Extended volumes.
The test results from AJA System test show that the speed of reading and writing from a single file is the same between APFS and HFS Extended. By contrast, the Finder copying tests show that the APFS can’t keep up when copying large numbers of files from one device to another. This is probably caused by the extra layers in the APFS file system, which are required to implement all the cool new features like copy-on-write and snapshots.
More on APFS: