How to know the sustained data rates of our SD cards?

4 years 4 months ago #665031 by ShutterPal
Speaking of memory card.  Is there a way to tell what the the sustained data rates are on our SD memory cards? As I understand, the read/write rates on the cards are best case scenarios, but are not sustained.  

So how can you tell what the sustained rate is?


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4 years 4 months ago #665045 by garyrhook
No, no one quotes "best case". They quote burst and sustained, and the manufacturers are very open about that.

There are also plenty of folks that test that sort of thing. Google it.

The only thing that matters is, will the write speed of a card keep up with my camera in an acceptable way? Everything else is moot, to me.


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4 years 4 months ago #665082 by Nikon Shooter
Buffer performance is the critical point in this, so
follow the camera maker's recommendations.

Light is free… capturing it is not!
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4 years 4 months ago #665097 by Marin Chi
+1 I was going to say the same thing about the buffer


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4 years 4 months ago #665106 by garyrhook

Nikon Shooter wrote: Buffer performance is the critical point in this, so
follow the camera maker's recommendations.


Well, you'd be incorrect when discussing SD media.

The bottleneck of any system where content is moving through a pipeline is the slowest element within that system. In the specific case of data in a compute system (which is what a DSLR is, at its core) the processor is fastest, memory is pretty fast, and storage is quite a bit slower. This is true for all computers. It's why things like SSDs and NVMEs were invented: to bring the speed of storage closer to the speed of memory.

So the buffer is not the bottleneck, the storage media is. You can test this be comparing cards with varying write speeds, and measuring how long it takes to clear a buffer full of shots.

Faster devices, such as XQD (which are PCI-attached) bring the speed of storage up to the speed of memory. Without any actual data to work with, we would then have to reexamine this different system to understand where the bottleneck would be. It may be the buffer. But it might just as well be the camera not being able to produce data quickly enough (i.e. frame rate) to stress the system and expose its shortcomings. Therefore, in this case: we don't know.


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4 years 4 months ago #665107 by New but trying
Sustained write speed is important for high bitrate video. Cards are often marked with a "V" rating which should tell your their sustained write speed.


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4 years 4 months ago #665110 by Nikon Shooter

garyrhook wrote: Well, you'd be incorrect….


I admit I was not totally precise when I attribute the transfer
rate to the buffer. I should have taken the time to elaborate
more — which I don't do as , contrary to you, I am not a good
typist — and attributed the writing speed to the OS of the ca-
mera. Now, if you don't mind… /

Light is free… capturing it is not!
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4 years 4 months ago #665118 by effron

garyrhook wrote: So the buffer is not the bottleneck, the storage media is. .


This 

Why so serious?
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4 years 4 months ago #665211 by Greg Friedman
Interesting, never really thought about this.  As already pointed out, can't exactly see write or read speeds jumping all over the place.  That would be frustrating!  


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