SanDisk 400GB MicroSD and Linux

📅 November 23, 2018
“400 GB on a MiscroSD card? Wow!”

MicroSD cards keep growing in capacity. The SanDisk 400GB MicroSD card packs more space than many hard drives onto a tiny wafer that a vacuum cleaner could easily swallow into oblivion.

Does this card work with Linux, and if so, what kind of performance can be expected? Here are my results.

(Nobody sponsors this. I am only sharing my results when using it with Linux in case this knowledge helps somebody else. The link to Amazon is a paid link intended to help others locate the item and to help support the time writing this article.)

Expecting Great Things

Like many of the items I test with Linux, I pay for them out of my own pocket. While the price was on sale at the time of purchase a few months ago, it was still more than most other cards, so this had better meet my expectations.

“Why 400GB? Who would ever use that much space on a MicroSD card?”

Rather than having several lower-capacity MicroSD cards and shuffling among them, why not use a single card that holds everything?

Besides, there is something called Parkinson’s Law of Data in the computer world where data expands to match the capacity of a storage device. This is why there will never be a hard drive with a large enough capacity.

Because of this, you can never have a MicroSD card that is “too big.”

The Card Itself

The package includes the card itself and an SD adapter. Text is complete with those dreaded asterisks that translate to, “We can’t guarantee what we said, so let’s provide a legal way out in fine print on the back of the box.”

Card Capacity

Windows 7 Properties. Out of the box, the SanDisk 400GB MicroSD is ready to use…kind of. It ships formatted in the dreaded, proprietary exFAT format. If you like exFAT, then all is good, but we Linux users need a more friendly file system to use with various devices.

“Why 366GB? I thought this was a 400GB card?”

Subtract 7% from the capacity quoted on the box, and you will get the real, usable capacity. This is true for any hard drive or storage device. Remember the asterisks on the box? The box quotes raw capacity (with asterisks), not usable capacity.

(400 – 7% is actually 372, so 366 is reasonably close. Linux reports a higher usable FAT32 space.)


CrystalDiskMark 6.0.2

Let’s perform a quick 5x100MB test in Windows 10 using CrystalDiskMark 6.0.2.

CrystalDiskMark 6.0.2, Windows 10. ~87MB/s read is expected based upon reviews I had read, but the 54MB/s write speed was better than what I was expecting.

This is a UHS-I, Class-10 card, so I was expecting a write speed of around 12-15MB/s based upon past experience with other cards. The 54MB/s is not screaming performance, but it is much better than the base Class 10 write speed.

MicroSD card speeds have progressed significantly. The SanDisk 400G MicroSD speeds are comparable to the 7200 RPM hard drive benchmarks shown here in Windows 7 with CrystalDIskMark 6.

Linux Performance

What does Linux Mint 19 say about this card?

Linux Mint 19 Disks shows 394GB exFAT, not 366GB as in Windows 7.

Windows 7 only provides NTFS and exFAT as formatting options, so Linux to the rescue! Linux Mint 19 provides the FAT32 format option.


Reformatted to FAT32 for better compatibility with various devices. Disks still reports 394GB of available space.

Disks 100x10M

This is colorful. Smaller file sizes tends to make the read performance jump. The card sustains about 88MB/s for reads and 75.4MB/s for writes when writing small (10M) files.

Disks 10x100M

Disks Benchmark reports an average of 88 MB/s for reads and 64.1 MB/s for writes. Writes tend to be more steady for larger (100M) file sizes.

In all of my testing, I never reached those magical “up to 100MB/s” speeds. (That’s why the asterisks and fine print are on the box.)

Note that in all cases, the SanDisk 400GB card was connected to a USB 3 port using a USB 3 card reader in Linux Mint 19, Windows 7, and Windows 10.


This is a good card!

I have not encountered any issues that would degrade performance. No bad sectors, no read errors, no write errors. It just works. Of course, exFAT is horrible to begin with, but when formatted to FAT32, every device I tried was compatible, and the full 366GB space was accessible. This might not be true with older MicroSD devices, such as the PSP, so experimentation is necessary.

For my uses, the SanDisk 400GB MicroSD is a solid performer and provides a large capacity for future growth. If you are need of a reliable MicroSD card with plenty of storage space, then this item is certainly one to consider.

Best of all, it works with Linux!


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