Storing data while sleeping

Hi all,

I'm wondering weather there is a way to keep storing data anywhere (on ram or onto other memory hw) while the mcu is sleeping ? Im asking that because Its really important for me to keep loging data but I can't keep the mcu alive all time because of battery issuing... My idie is to store data somehow anywhere (where?) all the time and waking up every X min/sec/hours in order to check the data...

Thanks