After a recent conversation on another forum about usage of the two card slots in the E-M1ii, I decided to try a test using the cards in hand. The setup I have been using since I got the camera is: Slot 1: Sandisk Extreme PRO 300MB/s UHS-II 64G for raw files Slot 2: Sandisk Extreme PRO 96MB/s UHS-I 32G for LF JPEGs The concept is to have the larger raw files on the faster card in Slot 1, and JPEGs in the slower card for both backup in the event the first card fails, and to be able to use the JPEGs while traveling for editing and sharing on my iPad. I ran five tests: Test 1: Slot 1 UHS-II Raw and Slot 2 UHS-I LF JPEG Test 2: Slot 1 UHS-II Raw and Slot 2 empty Test 3: Slot 1 UHS-I Raw and Slot 2 empty Test 4: Slot 1 UHS-II Raw and Slot 2 UHS-I Raw Test 5: Slot 1 UHS-II Raw+LF and Slot 2 UHS-I Raw For all tests: - I formatted the cards in camera before each test - The camera was set to High Speed @ 15 FPS - The camera was set for manual exposure and focusing: 1/50s, f/2.8 - The camera was on a tripod - I held the shutter for 30 seconds, and timed how long the camera took to finish writing to the cards with a stopwatch. - Timings for the frame rate were taken from the timestamps on the images to the nearest second; there may be some rounding, but it appears to be not significant. Here are some of the findings. - The camera never exceeded 12 FPS. There are a few seconds in all of the samples where either 11 or 13 images were recorded, but this is just rounding from the timestamps. - The best performance was in Test 2, using only the fast card: 155 total images in 30 seconds (5.2/sec) and 45 seconds until the camera finished writing (3.4/sec). About 60 shots in 5 sec before the buffer filled and the camera slowed down, running at 3.7/sec for the remainder of the 30 seconds. - Tests 3 and 4 were very close: 110/109 total shots in 30 seconds, 54/55 seconds to complete writing, about 50 shots in 5 sec until the camera slowed down to about 2.2/sec. This implies that the camera was limited by the slower card in either slot. I'd like to test two fast cards, but I only have one so far. It also implies that the camera writes simultaneously to both slots. - Tests 1 and 5 had the worst performance. Test 1 got less than 50 shots in less than 5 seconds before slowing down to 1.3/sec, completing 85 shots in the 30 seconds and taking 70 seconds to finish writing. Test 5 got about 50 shots before slowing down to 0.9/sec, completing 76 shots and taking 81 seconds to finish writing. Here are a few conclusions of mine. 1. There's a bit of marketing hyperbole going on with the 15 FPS second. The camera never achieved that with any configuration of cards, hitting 12 FPS in each case. 2. If you need pure speed, keep the second slot empty and use a fast card in Slot 1 (subject to my testing with a second fast card). 3. Writing raw to both cards is faster than writing raw to the fast card and LF to the second. Since the write speeds to the two slots are identical, the timing difference must be the JPEG generation process - either it's quite slow, or it's done serially and not simultaneously with writes to Slot 1. 4. Going to full flexibility - two copies of the raw file on two cards, plus a LF JPEG for SOOC sharing - really slows you down. In 30 seconds of shooting, you get 76 images rather than 155, and it takes 81 seconds compared to 45 to complete writing. This is not surprising, of course. 5. You get the maximum speed of 12/sec for at least 4 seconds in each test, achieving it for 5 seconds only with the single fast card in Slot 1. I'd be happy to have others make similar tests, perhaps with different cards. I'm going to order a second fast card, and I'll repeat the tests after that.