Why Is the Disk Space Usage Displayed in the File System Different from the Backup Size?

Symptoms

• Files are stored and backed up on a server. After a file is added or deleted, the size of the original backup does not change.
• The ECS backup size is larger than the used disk space displayed in the file system.

Possible Causes

The possible causes are as follows:

• The metadata of the file system occupies disk space.
• The disk is formatted. For example, after the Windows operating system is formatted, if writes have been performed to all data on the disk, then the entire disk needs to be backed up. In this case, the backup software compresses all-zero data.
• The backup software monitors the I/O writes to determine which data is changed and needs to be backed up. After a file is deleted from the file system, the file is recorded as changed data and will be backed up.