How to verify class speeds on a sandisk class 4 SDHC ?

I have two SDSDB-8192 cards which have “class 4” on the sticker.  
I noticed my camera giving an error with video, and even image storing taking longer. 

On putting each of them in a PC, I noticed that the read performance is closer to 1MB/s instead of the expected 4MB/s on BOTH cards. .
I verified that PC setup properly detects read performance of 4MB/s from both the HP L2531A that was in the camera and a Kingston 2GB microsd.  

I purchased these from a major retailer.  Is there a chance that these could be fakes? 
Is there an official way to verify these cards are performing to their labelled specification?

how are you testing the cards? you can use a free app called ATTO benchmark to test the speed of the cards. read and write performance should be at least 4MB/s

I have been using two methods -

  1. Crystal Disk Mark, Random Read test

  2. Using the “ReadyBoost” test in Windows Vista.

In both cases, these “Sandisk” class 4 devices consistently show about 1MB performance instead of the expected 4MB.

Does atto bench do random or sequential reads?

it does both. please post the ATTO test results

I can’t figure out to see how to get random reads with ATTO… it just gives one set of numbers that appear to match the sequential numbers from CrystalDisk mark

I managed to get a Sandisk 8GB card from a different lot for comparison as well. 

Sandisk 8GB  (marked class 4 - one of the “problem” ones)
0.5 1061 1337
1.0 1983 2037
2.0 3076 4005
4.0 4035 5377
8.0 4349 7249
16.0 4942 8070
32.0 5144 8965
64.0 5234 9269
128.0 5221 9348

Sandisk 8GB (marked class 4 - new one)

0.5 1210 1155
1.0 2027 2042
2.0 3996 4075
4.0 5950 6516
8.0 6927 10826
16.0 7638 14499
32.0 8500 17450
64.0 7289 20041
128.0 8898 20041

Kingston 2GB Microsd, class 2
0.5 1168 1318
1.0 1945 2002
2.0 3873 4035
4.0 6053 6472
8.0 7992 10755
16.0 8110 14435
32.0 8151 17368
64.0 8181 19889
128.0 8186 19889

HP 4GB  (class 4)
0.5 1086 1337
1.0 1936 2042
2.0 4005 4075
4.0 6385 6516
8.0 8982 10874
16.0 10218 14499
32.0 10272 17460
64.0 10886 20041
128.0 11014 19980

Is there that much variance in Sandisk cards, and both sets of numbers are right?  Could I have just gotten a couple defective ones?

Following up -

I have a set of Sandisk Class 4 SD cards which have random read times of 1MB/s, and one identical looking Sandisk class 4  SD card which is about 4MB/s random read.

I can’t exchange the opened SD cards at the retailer.  Can someone confirm that I can RMA these cards, or is this sort of variance expected?

here is the definition of SD class rating from Nowhere i can see that class rating refers to random read/write so i would say since the cards meet 4MB/s in your ATTO benchmark then no RMA would not be possible. also depending on the technology used in the card performance can vary.

SD Speed Class/UHS Speed Class

Greater Performance Choices

There are two kinds of Speed Class, “Speed Class” and “UHS Speed Class.”

As a characteristic of flash memory, actual transfer speed varies. Variable speeds are difficult to reliably record streaming content such as video because it requires a constant writing speed. Speed Class and UHS Speed Class provide the constant speed necessary for video recording by designating a minimum writing performance so that minimum and constant speed is guaranteed for camcorders, video recorders and other devices with video recording capabilities under the conditional write operation specified in the specification.

Speed Class, designated as Class 2, 4, 6 and 10, is designed for normal and high speed bus interface (mode) and UHS Speed Class 1 is designed for UHS-I bus interface*. (Speed Class and the UHS Speed Class are not compatible.)