are you using the ext4 filesystem? If you are not sure you can check by typing "mount | grep ext4".
If you are using ext4 then the failure appears due to a short IO wait time in the standard configuration of ext4. This causes the file system to automatically switch into read-only mode. To solve this issue please stop your virtual server and boot it into the Rescue System to make a file system check. If the command "mount | grep ext4" for example recognizes an ext4 filesystem at /dev/sda2, please perform the command "fsck /dev/sda2" After checking the file system you can boot the server normally into your standard OS. If you change the timout for your system, you can prevent this failure from happening again. To do that you can increase the latency via the command: echo 120 > /sys/block/sda/device/timeout This setting only stays until your next reboot. There are methods, depending on your OS, to making this permanent. If you are using Debian/Ubuntu for example, you can write this command in /etc/rc.local.