When you download Mist and try to sync the Ethereum blockchain, your Ethereum folder will be in the following location:
To save space, you can put your chaindata folder in another location such as a removable USB drive.
Above you can see my chaindata folder is actually a symbolic link. To create a symbolic link run this command:
> ln -s /Volumes/myUSBdrive/Ethereum/chaindata ~/Library/Ethereum/chaindata
What I’ve done is I’ve put my 39Gb chaindata folder on a thumb drive and I’m linking to it. The reason why it’s 8.43Gb is because I haven’t removed test net yet. Testnet is 8.24Gb. Once this is removed, even more space will be saved.
The other option is to create a symbolic link to the entire Ethereum folder but this results in an error where Mist is looking for a geth.ipc file which is created upon startup but it can’t because of the symbolic link. This is the easiest and quickest way to have the data directory located in a non default location.
This is different to bitcoin-qt where the location can be specified in the configuration file.