Has anyone had this issue where they are getting a The file could not be written to disk. error on ExpressionEngine v2.9.2. I notice I am only having this issue with files 2MB and up and in following other posts I have turned off XSS filtering with no help. If it means anything I have EE running on two EC2 instances that are being load balanced. Deployments are handled with OpsWorks. I have also increased file upload size and post size, as well as the ELB connection settings.
So I found the issue. AWS uses some sort of virtual /tmp directory by default. So I used the command df -h which showed me that my "overflow /tmp" directory was only 1M which is what caused the could not be written to disk error. After searching how to fix that I found that you could use sudo umount -l /tmp to unmount the current directory and then use sudo mount -t tmpfs -o size=10485760,mode=1777 overflow /tmp to make that directory 10M.
来源：https://stackoverflow.com/questions/34618271/i-am-having-a-the-file-could-not-be-written-to-disk-error-in-expressionengine