In my experience, one of the highest-impact upgrades you can perform to increase Raspberry Pi performance is to buy the fastest possible microSD card—especially for applications where you need to do a lot of random reads and writes.
There is an order-of-magnitude difference between most cheap cards and the slightly-more-expensive ones (even if both are rated as being in the same class)—especially in small-block random I/O performance. As an example, if you use a normal, cheap microSD card for your database server, normal database operations can literally be 100x slower than if you used a standard microSD card.
Because of this, I went and purchased over a dozen different cards and have been putting them through their paces. Here are the results of those efforts...
Visit TFA for the full table. The overall winner seems to be OWC Envoy SSD (USB), with hdparm buffered: 34.13 MB/s; dd write: 34.4 MB/s; 4K rand read: 7.06 MB/s; 4K rand write: 8.20 MB/s
takyon: The value winner in the article is the Samsung Evo+ 32 GB (purchased for $9.99 from Best Buy) with decent/passable speeds.
(Score: 2, Interesting) by Anonymous Coward on Friday December 04 2015, @08:24PM
It can be a significant issue when using sd cards in production with more complicated gadgets. For example, if you have a device which stores its fault log in eeprom, and it keeps writing to the fault log recorder errors which arise from the sd card being unable to handle the writes properly, it can blow your eeprom up as well.
When you're doing serious field work, you never want to skimp on your removable storage.
--Ethanol-fueled from the beach