Tag Archives: CrystalDiskMark

Sav’s guide to USB flash memory & Micro SD card testing

You just bought a new USB flash drive or Micro SD card, nice! But is it fake? Does it meet the advertised capacity and speeds? These things should be tested right away, giving you enough time to go back to where you bought it from if needed.

One of the most important things is how fast is the read and write speed of the port you’re using to test the drive. If you’re testing out an SD card, make sure the reader/writer is capable of going beyond the speeds the card is capable of.

If you’re unsure, just be aware that if your tests reach this number constantly then maybe it is your port and not the SD card. Assuming you’re not sure of the capable maximum speed, lets start off with:


Most cases drives come already formatted, so before making any changes, doing a quick test with CrystalDiskMark allows you to assess if your port that you’ve connected to is holding you back. Use another drive to compare it to.

I recommend making a folder on your desktop, with the folders nicely named of each drive you’re testing.

If you do not have a spare drive or SD card to compare to, then just be aware that if you just purchased a drive that claims to read and write 100MB/s and you’re only getting 30MB/s well that may be the maximum the port can go. You may need to try another device as an alternative method. This doesn’t mean it can’t possibly be that bad. It actually can, but this is all about getting a baseline for your tests.

Disk Management

See what you’re dealing with. Press Start (Windows 10) and run “diskmgmt.msc”, this will open up Disk Management and will show you what the partitions look like on the drive. If there’s two partitions, with one being very small I wouldn’t touch it for now, but simply make a mental note. You’ll start to get a better understanding of the drive as you go.


Once you’ve done a baseline and checked the size, the main thing to do is a data integrity test. This will save you the bother of continuing if the size (capacity) is false. It will also give you a average read and write speed, but this test is the longest.

If H2testw managed to successfully write every byte on the disk without issue then the capacity is real. It should have also given you a average write & verify (read) speed result while it was doing the test. Take screenshots and move onto the next steps.

SD Card Formatter

If you’re using an SD card, it’s definitely worth formatting using the SD Card Formatter tool from SD Association website. If the drive needs a format, this is reliable way to do it. I also like to run diskpart and clean the drive before doing a format.


Press Start (Windows 10) and type cmd which should result to Command Prompt. Right click and run as an administrator. Step 1) Type “diskpart” in the terminal and it should run. I’ll be basic with the instructions on this, but I recommend looking at a few YouTube videos of this command line tool if this is the first time you’re using it. Any wrong move and you might format important drives.

Step 2) list disk

You’ll get a nice list of all the disks connected to the system. Look for the one that is your drive you’re dealing with. Usually you can tell as it’s the last connected drive and matches the capacity.

Step 3) “select disk x(where x is your USB key)

Step 4) “clean”

HD Tune Pro

This program basically does what CrystalDiskMark does but gives some more information. I like to do a read/write tests without the drive being mounted (first tab). Take screenshots of both the read and write test.

Format the drive using SD Card Formatter / diskpart / Disk Management console.

If you’re formatting an SD card; use SD Card Formatter above. If it’s a normal disk or USB drive, you can use Disk Management to create preferred partitions or use diskpart again, repeat the steps above, but continue below.

Step 5) “create part primary”

Step 6) “select part 1”

step 7) “active”


Storage manufactures are basically falsely advertising by using a different form of measurement of bytes thus resulting in different outcome for what is the true capacity of the drive. To be as simple as possible. 1 GB to them is 0.9313 GB.

So an advertised 1TB would be 931.32GB on your computer as available storage. If you’re getting even less than this then the capacity is basically missing.

Here’s some useful information:

Why a hard drive has less storage space than promised?

Convert byte to gigabyte – Conversion of Measurement Units

SSD is 256 gb but only showing 238 gb? | Tom’s Hardware Forum


Using various software and tools mentioned above you can collect enough results to determine the true capacity and speed. There are more tools. There is more things to know, but for now this is it.