How to view the monitoring result of the subtraction of two items?

[Ales Ulrych]

Hello,
I'm new to this program, yet I am acquainted with him and some days I'm trying to figure out how to view the remaining space on the Synology NAS drive. I have solved connection via SNMP and disk capacity use hrStorageSize, for disk full hrStorageUsed. Now I would like to perform hrStorageSize - hrStorageUsed = FreeSpace that I'd like to see in the monitoring.
Now I can only display both items and in my head I have to calculate vacancy.

Trigger
Name: Free disk space in {HOST.NAME} is below $3% (Used {ITEM.LASTVALUE1} from {ITEM.LASTVALUE2})

Expression: 100 - (({nas2.interflag.local:hrStorageUsed.last(0)} / {nas2.interflag.local:hrStorageSize.last(0)}) * 100) < 15


You advise me whether the calculated result is something to show Trigger Name?

Thanks

Ales

PS: I would make sure that my question is understood, or really not my requirement solution?

Sorry for my English, I not control it and I write only with the help of Google Translator

[Ales Ulrych]

Nobody knows?

Nobody knows the answer or can not Zabbix do this?

[DmitryL]

Hello Ales,

You might use calculated item, to calculate ( total - used ) and then create trigger on calculated item.

https://www.zabbix.com/documentation/3.0/manual/config/items/itemtypes/calculated

[Ales Ulrych]

Hello Ales,

You might use calculated item, to calculate ( total - used ) and then create trigger on calculated item.
https://www.zabbix.com/documentation...pes/calculated

Thanks for the link,
This is what I've read, and I did some tests, but I'm not working.
Can you please send me a piece of code, how would you do in my job you applied?

[DmitryL]

If you have 2 SNMP items (1 for total and 1 for used)
last("exact_key_from_item_total")-last("exact_key_from_item_used")

This expression is Formula, not the item key.

So basically you need 2 SNMP type keys, lets say
key1 - to get total disk space using SNMP
key2 - to get used disk space using SNMP

Then create calculated item on same host and in formula field add expression:
last("key1")-last("key2")

[Linwood]

And on many systems you need to get the units of the first two as a third item as SNMP might not return bytes or megabytes. If all you want is percentages it doesn't matter, but if you want actual space you might need this. Check your MIB.

[Ales Ulrych]

And on many systems you need to get the units of the first two as a third item as SNMP might not return bytes or megabytes. If all you want is percentages it doesn't matter, but if you want actual space you might need this. Check your MIB.

I know that I've already solved

[Ales Ulrych]

If you have 2 SNMP items (1 for total and 1 for used)
last("exact_key_from_item_total")-last("exact_key_from_item_used")

This expression is Formula, not the item key.

So basically you need 2 SNMP type keys, lets say
key1 - to get total disk space using SNMP
key2 - to get used disk space using SNMP

Then create calculated item on same host and in formula field add expression:
last("key1")-last("key2")

Thanks, I get it working.