Hello,
Welcome to the forums. Will you please provide more information.
The basics;
What phone do you have?
What version are you on?
About your problem;
Does your device have an SD card?
What size is your SD card?
Has it ever worked or did this just start?
Do you have any apps that might affect how the SD works, something to compress space, clean partitions, encryption etc?
When do you get the notification? At start up, randomly, when you open an app, when you look at pics?
Can you see anything stored on the SD before or after the notification?
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