Re: OpenNMS Disk Percentage graph showed incorrect value
On UNIX-derived systems, some filesystems are created by default with a percentage of space reserved for the root user.
'df' reports available space *excluding* that percentage.
OpenNMS calculates usage from the size of the filesystem and the blocks reported as in use - excluding the 5%, as the SNMP daemon usually reports values exclusive of that.
If you look at your numbers for 'available' and 'used' in the output from df, they do not add up to the total number of blocks. In your case, the raw maths on blocks comes out to 71% used, 21% available - yet df says 78% used.