64GB StorEdge Speed Test on 13" Retina MacBook Pro
Installed 64GB PNY StorEdge on my Late 2013 13" Retina MacBook Pro yesterday - as others have noted, it protrudes about 0.25" due to the short slot on these machines. I ran BlackMagic Disk Speed Test on it without reformatting the card - WRITE/READ 5GB test file every 8 seconds. The first few W/R cycles showed a low write speed (~10 MB/s). When I stopped it about 10 minutes later, the last test cycle showed 51.2 MB/s WRITE and 72.8 MB/s READ.
I then used Disk Utility to format it as HFS+ Journaled - GUID and ran the same speed test. It started off with low write speeds (~10 MB/s) but high read speeds (80 MB/s). The connection to the card was lost during the testing, but it spontaneously remounted. The connection was lost again a little later; removing and reinserting it did not remount it. I had to reboot the computer.
Concerned about the integrity of the card, I decided to perform more systematic formatting/speed testing. I reformatted it as exFAT-GUID (similar to out-of-box format) and ran 25 cycles of speed testing (5 GB file size). The average speed +/- standard deviation was 37.4 +/- 14.4 MB/s WRITE and 76.0 +/- 10.8 MB/s READ. I then formatted it as HFS+ Journaled-GUID and repeated the 25-cycle speed test: 50.1 +/- 6.7 MB/s WRITE and 85.7 +/- 2.5 MB/s READ. I concluded that HFS+ was the preferable format based on the higher averages and smaller deviations. My observation is that the write speeds for the first few cycles are typically low regardless of formatting.
I then copied 60 GB of small files to the card and used Activity Monitor to keep track of progress. The copy started at about 10 MB/s write speed and the operation was predicted to take 2 hours to complete. The write speed gradually increased to 60-75 MB/s and the estimate dropped to 30 minutes. After transferring 35 GB the speed suddenly dropped to less than 1 MB/s for several minutes before picking back up to 60+. The write speed throttled back to near zero several more times before the operation was completed. I suspect Mavericks software is implicated rather than the SD card. In all, the 60 GB of small files was copied in about half an hour - very satisfactory in my opinion.
One negative Ive noticed is that every time Ive closed the laptop lid for extended periods of time (deep sleep), the SD card is disconnected and the inappropriate removal warning is displayed when the lid is opened and the machine is awakened. Removing and reinserting the card is needed to remount it. I dont know whether this is a Mavericks issue, a USB-3 issue, or a SDXC issue.