Y axis not converting bytes to TB properly

Hi everyone

New to Grafana but I did Google a bit around my issue but came up empty.

So I’m playing around trying to learn telegraf+influxdb+grafana and as a start I enabled SNMP on my QNAP NAS to pull some metrics from it.

I’m struggling a bit with understanding how Grafana converts from bytes to TB.

Ok, first off, here’s a sample of the data I have:


The MIB file defines the object sysVolumeFreeSizeEX as follows:

sysVolumeFreeSizeEX OBJECT-TYPE
SYNTAX Counter64
ACCESS read-only
STATUS mandatory
DESCRIPTION “System Volume free size in byte.
::= { sysVolumeEntryEx 5 }

Ok, so as an aside, the MIB file seems wrong because the values actually look like they’re in kilobytes. In any case, when I bring the data into Grafana, I just multiply them by 1024.

So in Excel, I just did a crude calculation to go from bytes to KB to MB to GB and then finally to TB (dividing by 1024 each time).

Here’s what that looks like:


And if I log in to my NAS, this is what it shows me for free space:

https : // puu . sh / B1eHz / efd9b3aede.png

So my calcs match what the NAS is saying.

But here is the Grafana number for GB:

https : // puu . sh / B1eKj / 15b3d0b334.png

Here’s the data source setup where I bring the metric into Grafana:

https : // puu . sh / B1eLN / 5c668e2b61 . png

And here is where I choose the unit for the axis:

https : // puu . sh / B1eQQ / f68aa7ae76.png

I cannot understand how Grafana gets 1.3873564TB.

Apologies for messing up the links but new users can only post 2 links max.

You should select the unit in Grafana which reflects the resolution of the data returned not what you want to visualize - Grafana will automatically adjust to TB for example. So you shouldn’t need to multiply with 1024.

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