128gb Ultra slower than class 10 write

My Sandisk Ultra micro sd was taking a long time to transfer files. I’ve looked into the problem and now done the following,  performed a full format in exfat with SDFormatter,  then peformed a full write/read test in H2testw. 

The write speed as reported by H2testw is 5.54 Mbyte/s, well below class 10 minimum of 10 Mbyte/s.

Question is can I apply for replacement and begin RMA  process? I’m in the UK and bought from Amazon


in that case i suggest testing the speed of the software with the official crystal disk mark software that is also recommended by sandisk to see the actuall speed of the card. If then the write speed is under 10mb then of course you can ask for a replacement if not then the card seems to work normally

here you can download the software to test


I filled in the online RMA request, was asked to show a screenshot of the test result from Crystal Mark, and subsequently RMA was authorised. The slow micro sd card is on its way back for replecement now.

If anyone else has a suspicion their card is underpeforming I can recommend the online process.


that is very good to hear that and i will keep that in mind