I have a Roku Ultra, 4660RW, that I have a 4 GB micro SD card. I was troubleshooting another issue and noticed it was not showing up as installed on my device. I powered down the Roku, then pulled and reinserted the SD card, then powered it back on. Still was not recognized. So I pulled the SD card with the Roku powered on and then it recognized SD card but suggested it needed to be formatted. So I went ahead and let if format it.
When the formatting was done it is showing using 6% of the SD card.
Not sure why the SD card stopped being recognized and do understand that things sometimes glitch. But as far as I could tell from operation nothing to me seemed to be affected by the failed SD card. So wondering what might be some indications of a failed SD card? I don't have a ton of Apps installed but it's enough to have to use 6% of the SD card. Does the Roku give a message of not enough memory or something similar?
They do seem to get corrupted sometimes and can cause strange issues when they do, but I don't think you ever get any kind of notification about it. As you've observed when it wasn't recognized, they're not really necessary. I think the only message you'll get concerning the SD card is the one that says something like, "You may want to insert a microSD card...". You get that when it has to remove the code for an app to download another one. If you only have or use a few apps then you won't see that message very often if at all. I've never felt the need for one myself.
Back when I was running a Roku 3, I used to use an SD card in its SD slot. The only thing it is used for is to expand the Roku's channel storage capacity . And no matter how big the card, the Roku won't use more than 2 GB of the card.
On more than one occasion the card got corrupted, causing the Roku to get stuck on the bouncing letters startup page - removing the card would let it start up normally and go to the home screen. I had to reformat the card in my computer, then put it back into the Roku and let the Roku reformat it again for it to work. After several cycles of this, I just decided the hassle wasn't worth it and left it out.
Today's Roku product line have MUCH more channel memory storage than in the past, and SD slots are absent from all current players.