Filesystem becomes readonly.

Hi LUVers 1.Linux (Debian Wheezy) running on a cloud server 2.Everything working fine for weeks/months 3.Last nite, for some reason all disk writes to server stops 4.Even root cannot write to anywhere on the disk, and plenty of space left on disk (~80%) All file permissions look OK. 5.After reboot all return to normal.(ie problem is fixed) My questions: Is it fair to assume that the problem was caused by something that the cloud provider has done? Or could it be something on server OS side? What can cause this? (I am thinking the virtual disk hosting the VM has become readonly somehow, but how? ) Cheers Daniel.