Sandisk 32GB Ultra Class 6 (20MB/s) SDHC Memory Card


The read speed is at around 18MB/s, but the write speed tops at around 7MB/s using H2testw 1.4 in an internal card reader / writer (Windows 7 x64, 12-core processor).

Is this normal for this class of cards?


Some class 6 cards might only be written to at around 7MB/s , while some class 4 cards might be written to at 6-8 MB/s at times. How does this test work? I noticed that with larger sized files I achieved higher write speeds.

i guess yourclass 6 card is doing okay if you get write speeds over 6 MB/s. I was surprised when I got write speeds in the 7-8.5 MB/s range with a class 4 card. One class 10 card(not made by Sandisk)  had write speeds in the 8-8.5 MB/s region, with medium sized files. That was not good.

Thanks for confirming.

I’d have gotten a CF for $15 more.  Oh, well.

I just noticed in the title of your post 20 MB/s. Perhaps that might be the read speed? I would think if the write speed is stated as 20MB/s, then the card should be listed as class 10.

Well, its package states the card as Class 6 x133.

Your internal card reader might also be slow. Perhaps the card might perform much better in a fast USB card reader? I also noticed that with the same card and card reader I had very different write speeds on different occasions. Did you do the test while multitasking? Perhaps you should try writing some of your own files to the card and see what write speed you get. I noticed  little difference in write speed between the class 4 cards and class 10 card. What size were the files being written? Writing many small files is much slower than writing a few large files. 

I think it might be the reader, too… but it’s connected via USB internally.

I did try copying files manually, but it’s even slower.

Oh, well.

These cards perform better with large files, right?

“These cards perform better with large files, right?”

That is what my tests showed. To see this in the extreme, I backed up my favorites to a flash memory card. I have many favorites on my pc. Each file is less than 1,000 bytes. I think the speed when backing up a large number of these was under 1 MB/s, while backing up large files with the same setup was over 7 MB/s.

Thanks for your help. :slight_smile: