Technical question on CF cards

[Luigi Bianchi]

Hello everybody

I want to buy a CF for my 5D3 and I came across a German newspaper which run a very detailed speed test on SD and CF cards:

http://www.chip.de/bestenlisten/Bestenliste-Compact-Flash-Karten--index/index/id/1002/

Up to now, my criteria when choosing an SD or CF was just the write speed.
However, I noticed that in this test they list also "access time" and "IO/s" (which to my knowledge are important for computer hard drives). As I am interested only in the camera being able to write as fast as possible to the CF, are those criteria important for me?

I have compared two cards with an affordable price: the Hama looks as having a faster average writing speed but then has poorer performance for average write access time and average write IOs.

Transcend CF Premium 800x 128GB:

average write data rate: 70,9 MByte/s
average write access time: 17,15 ms
average write IOS: 58 IO/s

Hama CF 128 GB:

average write data rate: 90,0 MByte/s
average write access time: 428,24 ms
average write IOS: 2 IO/s

As said, what are the most important criteria to look at, except the fact that here in CH the Hama is 35% cheaper? ;-)

Kind regards
Luigi

 

[Mark S Abeln]

Transcend CF Premium 800x 128GB:

average write data rate: 70,9 MByte/s
average write access time: 17,15 ms
average write IOS: 58 IO/s

Hama CF 128 GB:

average write data rate: 90,0 MByte/s
average write access time: 428,24 ms
average write IOS: 2 IO/s

As said, what are the most important criteria to look at, except the fact that here in CH the Hama is 35% cheaper? ;-)

I used to do computer performance analysis, and the general answer is “it depends on your workload.” But for photography, fast IO is usually needed as well as fast write data rates.

An IO is a single data operation where the camera says ‘write this block of data to the card’ and the card does so — but it doesn’t tell us how much data is being written, or how fast it is written. When a camera saves an image to card, how many IOs does it take to do this? One or many? If we assume that it only takes one IO, then we can say that the Hama card might only write two images per second at the most — no matter how tiny an image might be, like a highly compressed small JPEG.

The write access time is basically the reciprocal of the IO per second rate. 1/17.15 ms = 58/second. 1/428.24ms = 2.3/second. This will severely limit your ability to capture bursts of images, and every photo will take at least a half second to save to the card — or more, if the camera happens to use more than 1 IO to do the write.

The IO rate may be lowered greatly if the amount of data written per IO increases significantly. Unfortunately, the data doesn’t tell us how much is written per IO. But often, manufactures use the best possible situation, where only a small amount of information is being written at a time. We simply don’t know what is the situation used here.

OK, both cards have a write data rate speed within the same ballpark of each other. But that the Transcend has much faster access times and IO/second makes the Hama card seem rather suspicious. I would get the Transcend if I were to choose only based on this data.

 

[Mark S Abeln]

One Amazon review for a Hama card says that “it is the slowest card I own”. But I didn’t find reviews for your particular card.

 

[Luigi Bianchi]

Hi Mark

Thank you very much for your clear and easy to understand explanation, I have learned somethng new


I also looked at the measurements below, which makes me unsure:

Transcend:

Minimal write rate 30,63 MB/s
Max write rate 80,7 MB/s

Hama:

Minimal write rate 8 MB/s
Max write rat 131 MB/s

It seems that Hama excels in the max write rate but in the min write rate is very weak.

Anyway, I do not want to go into any risk as sometimes having the possibility to shoot bursts of images is important. I am using now SanDisk Extreme 120 MB/s and I will keep buying those.
This SanDisk is not the fastest card but it let me take a burst of about 22 raws before it slows down and from that point it takes about 5 seconds to clear the whole buffer.
Sometimes I shoot a burst of 10-12 images and then let a few seconds pass over until I find the next target for another 10-15 images and so on. In this case I never have to wait and the camera never slows down. This is a good speed for me and the price of the SankDisk Extreme 120 MB/s is acceptable.

Kind regards
Luigi

 

[Brad Morris]

The kamerabay x1066 cards are a favourite of the 5diii crowd shooting raw video using magic lantern.

They are cost effective and can keep up with the constant 100MB/s write speeds needed to output the raw video files.

Maybe worth a look on eBay.

 

[dosdan]

Hama:
Minimal write rate 8 MB/s
Max write rat 131 MB/s

It seems that Hama excels in the max write rate but in the min write rate is very weak.

Sounds like a write buffer in the CF cards speeds up the initial writing performance, but as soon as it fills, it bogs down to the unbuffered rate.

Or perhaps these write speeds are with different block sizes, hence the spread in speeds.

You could try an EXT USB3 card reader and HWTESTW. I fill my 64GB Sandisk Extreme Pro SD card completely with 1GB test files, and it doesn't slow down at all during the testing process. So it has a damn fast writing speed.

Dan.

 

[Luigi Bianchi]

Hi Brad

thank you for your advice. I found those cards on ebay but the correct name is Komputerbay.

Regards

Luigi