SD cards can be used for long term storage but only if you have a desire to lose the files and anger your clients. Master files should be considered as valuable as cash, since that’s what they represent, assuming you’re being paid for your work.
Offload those files onto a hard drive, one that is dedicated to storage only. Best practice for backing up data says store another copy of your files offsite or in the “cloud.” Cloud storage providers are everywhere. If you have gigabytes of files, search Google for a cloud storage provider that meets your needs, storage-wise and budget-wise.
