ONTAP Discussions

Get- NCEfficiency output discrepancy


Customer told me this - has anyone seen this?


Get-NcEfficiency should output "Used" "Returns" and "Effective Used" where Used = Used Data Capacity, Returns = Storage Efficiency Savings, Effective Used = Used + Returns.

Instead, the output for Returns is what should be the output for Effective Used. The actual Effective Used output does add Used + Returns, which means we can get the data we want with powershell, but using the wrong fields. This is most apparent with vol_xxx_Transfer which consumes 1 GB, has no savings from storage efficiency but reports 1012.7MB returns and 2.0 GB effective used.


This was their problem:


The customer is trying to track the amount of data they are loading into NetApp storage and then continue to accurately report on that data size as data is added or removed. The numbers they are trying to report on should ignore any deduplication or compression by NetApp.
They're planning to make use of the PowerShell DataOntap module to automate reporting.

They are seeing these numbers in the web portal (screenshot attached):

•Before[Hypothetical]: Data Space Used: 29.59 TB
•After: Data Space Used: 14.93 TB

And, they see these numbers from the PowerShell DataOntap module (screenshot attached):
•Used: 15.5 TB
•Returns: 29.6 TB

They're not sure which number(s) they should be using. Some of the numbers appear to possibly contradict each other, so they're just trying to get clarity around what the numbers mean and how they can report accurately on the current size of their customer's data.



This seems to be still so even 5 years later (DataOntap PS module 9.8.0):
df -g -S <vol> shows:
Filesystem used total-saved 
/vol/<vol>/ 1365GB 441GB 

Get-NcEfficiency -volume edmadat1 | select used,EffectiveUsed,Returns

Used : 1365 GB

Returns: 1806GB

EffectiveUsed: 3171GB

So returns=used+total-saved and EffectiveUsed=Used+Returns=2*used+total-saved=useless.