CF cards are not always what they appear to be

Update: The Sharpen card failed to write part way through an important photography trip, and then bricked itself on a format. Don’t buy it.

Recently, I travelled to Amsterdam and I made the foolish mistake of leaving my CF card in my reader, thousands of miles away in San Francisco.

I shoot with professional gear, and my Canon 5d MKII demands high speed CF cards. After failing miserably to navigate the canals, I found the local camera shop and inquired about CF cards. The woman began by quoting me insane prices. A Sandisk Extreme Pro CF card at 64GB began at a ridiculous 280€.

The woman pointed to a box and said “’You know, you could always just buy the special we have”. The special was a “Sharpen 64GB 120MB/s 800x UDMA6 CF Card” at the low, low price of 1€/GB with a free reader.

64€ sounded much better than 280€, and when I was I going to be back in Amsterdam again? I had to take photos now, so I bought one. It even came with a free reader, which appeared to be a USB3.0 reader with a blue plug. All nine pins are visible inside of the device, so it must be true.

I’ve been relying on my SanDisk USB 1.0 “Thunderbolt” (the product name, not the cable type) adapter for years now. I had no idea how bad it’s performance was (see below) It’s garbage, and I’ll never use it again.

Off to the blumenmarkt I went, camera in hand, riding a shiny red rental bicycle. (It had one of the most ridiculous anti-theft locking mechanisms on it, but if you’re interested in that, click the link.)

After many pictures of pretty canals, I came back to SF. What had I purchased? What is this blob of black plastic actually doing inside? Onto the test bench with it for exploratory surgery and testing. Did I get screwed?(Spoiler alert: I didn’t.)

Using the excellent and free Black Magic Disk Speed tool, I started running numbers.

Test Setup

My test setup was a Mac Pro (late 2013, 3.5Ghz 6-core Intel Xeon E5, 64 GB RAM, 6TB RAID5, 1TB Internal Hybrid SSD.)
CF adapters were directly connected to the USB ports on the back of the Mac Pro. The Mac Pro supports USB 3.0.

It’s good here to remember the maximum speeds for USB, and CF cards
USB 1.0: 12MB/s
USB 2.0: 480MB/s
USB 3.0: 4.8GB/s
Compact Flash “speed cap”, all cards, all protocols: 167MB/sec

Test Results

Card A: SanDisk Exteme Pro Compact Flash, “90MB/s 32GB, UDMA6”
Write: ~50-60MB/s 
Read: ~70–73MB/s
(Connected via the Sharpen USB 3.0 adapter)

Card B: SanDisk Extreme Pro Compact Flash, “160MB/s 32GB, UDMA7”
Write: ~43.3MB/s 
Read: ~70.1MB/s
(Connected via the Sharpen USB 3.0 adapter)

Card C: Sharpen Professional Compact Flash, “120MB/s, 64GB 800X UDMA6”
Write: 87.7MB/s
Read: 120.1MB/s
(Connected via the Sharpen USB 3.0 adapter)

In comparison, my Promise Pegasus2 R4 RAID5, which is my main photo storage array is around 365.5 MB/s write and 533MB/s read across four drives.)

The Mac Pro’s Internal “Hybrid” SSD storage (SATA) is even better at 972MB/s write and 872.2MB/s read, crushing the spinning disks of rust that is the RAID5 array.

Installing the “Thunderbolt” USB 1.0 adapter limited all results to 10–12MB/sec write and 12MB/s read regardless of the card used. It’s been good to me, but sorry old friend, you’re headed for the recycle pile.

Some Conclusions

SanDisk, or the vendor, lied about the card speed or does not test: When I first bought my camera I bought Card A. Card B was purchased a few weeks ago, and both were purchased from Amazon. Card B is the worst performing card that I own, clocking in well under the Card A by nearly 30MB/s. Why is a card, that is significantly more expensive and running UDMA7 with a claimed speed of 160MB/sec, outperformed by a UDMA6 card with a quoted speed of 90MB/s? Maybe the vendor ripped me off with a relabeled card?

Always use USB 3.o: I should have switched to USB 3.0 sooner. I had no idea how slow the old reader was. Lightroom imports took for ever and now I know why. Also, never transfer over WiFi, it’s a joke. I have no idea why there are some readers on the market with this feature.

No matter what, get yourself a USB 3.0 CF Card reader if you’re shooting on a regular basis. It will save an incredible amount of transfer time.

The compact flash format is obsolete and high end cameras need to move off of it: The speed cap at 167MB/s is detrimental to video and the new uses people are finding with cameras. Recording at 4K is not possible at this rate, and SD cards here are the only way to go. If you buy a UDSII, class U3 card, you’ll see up to 250MB/sec write speeds and 280MB/sec read speeds.

There’s a reason why the EOS 1d X mark 2 has a CFast 2.0 slot (500MB/s read performance.) The speed cap is a killer.

My tests are largely incomplete and could have been done across many more readers and cards: Yeah yeah, I know. You work with what you have and this testing is mainly for my use. You’re welcome to make decisions on it, but there are better places to look at for speed comparisons.

Anyhow! Go take some photos.

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