Any recommendation for SD Card speed / class?

Hi folks,

The SD card in my RPi Model B running EmonBase seems to be on the way out, so I need to get a new one, and was wondering if there is any recommendation on what speed / class is needed? I only have two feeds and and running in low write mode, and the only extra applications are Monit and Node Red + Python script for controlling some lights. Is Class 4 good enough, or should I look for Class 10?

And any thoughts about using a Micro SD Card in an SD Card adapter compared to a real SD Card? I only use SD Cards in the Model B, and if/when that fails, the SD cards would be useless, whereas MicroSD cards could still be used in my Pi3 and Pi Zero, but if the adapter is a weakness then I will happily just stick to SD Card.

I thought I remembered this being discussed ages ago but I couldn’t find anything on the forum, or in the install guides, so thought I might as well ask :wink:


Hi Ian, I don’t think the class/speed is overly relevant in normal running of an emonBase and even less so if running read-only.

I recently changed my preferred brand from a class 4 Samsung to a class 10 Sandisk after supplies of my “usual” dried up. When I previously moved from one Samsung class 4 to another Samsung class 4 of the same size etc, I found them painfully slow with loading the initial image despite being the same spec, same image, formatter and imagewriter, I never did find out why, I tried several suppliers and ended up changing to a Sandisk.

So spec’s aren’t totally reliable and it’s worth sticking to a known model if you find one you like.

My current favorite is SanDisk Ultra 8GB microSDHC 48MB/s Class 10 UHS-I Memory Card
Although it was well over a quid cheaper here when I bought my last batch, so it’s a tad expensive now.

IMO the only weakness of the SDcard or microSD adapter on the Pi B is the fact it sticks out so far, so if you do go down the route of an adapter, try a half size metal frame adapter rather than a SDcard sized adapter.

I use this type with a hinged/locking mech
There are also end on slot types that mimic better the micro sd slot on a later Pi, i guess these can be better if you are moving the card a lot. Low-profile microSD card adapter for Raspberry Pi : ID 966 : $2.50 : Adafruit Industries, Unique & fun DIY electronics and kits

Hi Paul, Thanks for the detailed response - I didn’t even know about half size adapters!