Is that just me or do I have a particularly crappy SD card? Anyone got any tips on how to improve disk IO? Would a USB3 external drive help with this?
Emphatically yes. It's an entirely different experience using a RPi 4 with a quality SSD. [0] It's also more expensive, so you have to decide whether that's important to you.
[0] https://www.samsung.com/us/computing/memory-storage/portable...
In my opinion it's a mistake to split the difference with a cheap SSD or one you need to plug in using a SATA to USB adapter. (troubleshooting first step: if it's not the power supply, it's the SATA to USB adapter...)
USB3 could plausibly be faster than the SD card as the spec allows for 5Gbps+ but I don't know about Pis that much, I'd defer to someone with experience.
As a photographer I can tell you that SD cards, even high class ones have laughably awful speeds - any proper camera that needs to do video will use CFexpress Type B cards which are tremendously faster.
Seriously though, there are plenty of top-end cameras that use SD cards (all Nikons, for example).
EDIT: completely missed that you said video, ignore me!
That won't help OPs Pi4, the PCIe interface is new on the Pi5. USB is the best you can do on the older ones.
Using an external USB3 drive also helps but it's still pretty slow. I found it too slow to use as a SAMBA file server when connected over WiFi, even though it was hardly pushing the CPU or memory. It would regularly fail to transfer large files.
One of the main selling points of the Pi 5 is faster IO. I'd love to see something tiny and power-sipping like the Zero but with the enhanced IO of the Pi 5.
My OS however is in the SD card which is Sandisk which I assumed was the good fair price brand.
[1] https://en.wikipedia.org/wiki/SD_card#Application_Performanc...
After, "sudo apt-get install preload" it will cause previously used programs from the last session to auto-cache into ram. Combined with the above setting, the usual programs will launch much faster.
There is also the option to use an external SSD drive for better performance.
Part of the fun of pi4 was getting the OS optimized, but unless you have a legitimate "Sandisk Extreme Pro U3" or >30MB/sec rated sdcard it can still be slow (people have seen 4MB/sec on old counterfeit cards.)
sdcard bus overclocking is a thing as the pi tries to maximize slow hardware compatibility by default. Note this feature is limited on the pi4, but can significantly decrease boot times on older models.
YMMV =)
On Pi 4 I use a 2.5" SATA SSD (WD blue) on a startech USB3 adaptor and the performance seems to me much better than even good quality microsd cards.