SD Card defragmentation!?

Hard drives need to be defragmented because they can read data quickly if it's written as a continuous line. The read/write head stays in one spot as the platter spins underneath it. But if the data is fragmented, the read/write head has to move back and forth and wait for the next chunk of data to spin underneath.

Solid state media like flash drives don't have this problem. They can access all parts of storage at the same speed so it doesn't matter if the data is stored in physically continuous memory cells, or if it's all scattered around.

What kind of SD card did you get? Most people make the mistake of getting the highest speed card they can find. The problem is, the speed ratings on these cards are for sequential (one large) file access. That's the speed that matters if you're writing video or large digital camera files to the card.

Unfortunately, tuning a card for fast sequential speeds often means compromising its speed for small file access. A lot of the class 10 or faster cards have 20 MB/s or faster continuous read/write speeds, but atrocious 4k speeds far slower than 1 MB/s. Some of these cards can't even hit 0.005 MB/s 4k speeds. If you've ever tried to copy a folder with a bunch of MP3s to a flash drive and Windows says it'll take 10 hours, it's because you've got a flash drive which has been tuned so much for fast sequential speeds that the 4k speeds are glacial slow.

4k speeds matter a lot more for general computer use (like games) because that's the size of things like configuration files and log files. The class 4 or 6 cards tend to be tuned for better 4k speeds, at the cost of slower sequential speeds. Unfortunately, as the market has been driven by advertising for fast sequential speeds, and manufacturers have not given much love to these slower cards. I don't think you can even find any new class 4 or 6 cards for sale anymore - everything is old stock 3+ years old.

When you're buying a flash drive or SD card, I would recommend searching their reviews to see if anyone has done full benchmarks on them. Sorting the reviews by most helpful first often brings any benchmarks to the top. Otherwise you can search for CrystalDiskMark - that seems to be the most popular benchmark. A full set of benchmarks will tell you the drive's sequential speeds, 512k speeds (good estimate for speed reading/writing MP3s and JPEGs), and 4k speeds (Office files, config files, text files). Make sure the drive is fast across all these speeds before buying it, not just sequential speeds.

I've been doing this for close to a decade to filter out flash media with unacceptably slow 4k speeds. SanDisk consistently has the best flash cards and flash drives for general-purpose computing. Their high sequential speed cards are usually also able to manage at least 1 MB/s 4k speeds (which is about the same as a HDD). Some of them even manage 2-5 MB/s 4k speeds (which makes them faster than a HDD). I've got a SanDisk USB flash drive which gets 180 MB/s sequential speeds and 10-15 MB/s 4k speeds - that makes it faster than a HDD (typically 125 MB/s sequential, 1 MB/s 4k) and more like a slow SSD (typically 500 MB/s sequential, 30 MB/s 4k). Somehow they managed to do this without resorting to adding a SSD controller to the flash drive.