topic Understanding Storage Size Values in ONTAP Discussions

Understanding Storage Size Values

DBWannaBe — Wed, 04 Jun 2025 10:08:01 GMT

My environment:

VMWare vCenter 7.0.3

EXSi host 6.7

Ontap 9.8p5

I have a lun that is 2TB in size as reported by Ontap.

ESXi sees it as 2TB that has 507GB of unused space.

Ontap sees it as 2TB that is 100% full.

The volume only has the 1 lun attached to it and is not protected with snapshots.

Ontap reports the volume as 4.5TB in size with autogrow turned on.

Ontap further reports that the volume only has 519GB of available space.

My question are; Why is the volume so large? Where is the extra data coming from?

I'm pretty new at this but this doesn't make sense to me. It's also not just this one volume; I've checked and found a few more that follow this basic pattern.

Thanks for any help.

-Mike

Re: Understanding Storage Size Values

pedro_rocha — Thu, 02 Dec 2021 19:40:49 GMT

Possible cause to this is fractional reserve. Probably it is set to 100% (default).

https://docs.netapp.com/us-en/ontap/san-admin/set-fractional-reserve-concept.html

Since you do not use snapshots for this volume, you can try to set it to zero a check if space available in the volume will increase:

volume modify -vserver svm_XYZ -volume vol_XYZ -fractional-reserve 0

Re: Understanding Storage Size Values

DBWannaBe — Thu, 02 Dec 2021 21:00:05 GMT

Yep, that was it! Thanks!

I set the fractional reserve to 0 and gained about 2TB of space back.

-Mike