We have a tag for hard-drive but nothing for "storage" or "sdcard". Adding this tag should make it easier for folks to find questions similar to the one they're asking which will hopefully reduce duplicates or make them easier to find. Given that we have 228 results for "sd card" it seems like there is enough critical mass for this tag.
I also considered tags like "capacity" or "specifications" which we don't have, but making it more specific and real world seems like it would be more likely for folks to find and use it easily.