A while ago I thought it would be a good idea to make a backup of my Linux server by just dumping the complete disk to a file. In retrospect, it would have been much easier had I just dumped the individual filesystems.

When I finally got around to using this backup, long after the 10GB disk had perished I realized that to use the loopback device to mount a filesystem it actually needs a filesystem to mount. What I had was a disk image, including partition table and individual partitions. To further complicate matters the data partition was also not the first partition inside this image.

When using the ext2 or ext3 filesystem by default 5% of the available blocks is reserved for use by the root user. This allows the system to continue running if non-root users fill up the file system and also assists in preventing file fragmentation because the filesystem does not fill up completely.