Suppose that you want to create a low threshold expression based on ns-dskPercent, to retrieve the available space on a file system, in order to generate an alarm when the value is lower than X, we should use an expression like the following:
100 - ns-dskPercent
This expression will be parsed like this:
100 - ns - dskPercent
The problem is that the variables "ns" and "dskPercent" don't exist and the threshold won't be processed.
The character minus confuses the expression parser and should be avoided on any mibObj. Searching the current content of datacollection-config, I found the following list of invalid mibObjects:
The solution is just rename the alias but that means all people that are currently using those mibObjects will lose their historical data. One idea to deal with this problem is to adapt Ben's conversion tool to remediate the ds-names in existing rrd files.