topic Re: Why is the capacity displayed differently on the server when configuring the volume? in ONTAP Hardware

Why is the capacity displayed differently on the server when configuring the volume?

rick2004 — Wed, 04 Jun 2025 11:15:58 GMT

Hi,

I configured 100000 GB vol1 on FAS8040.

However, when the server checks the volume, the visible capacity is 86.7 Tb.

Can you see why the capacity looks different?

Below is the volume information.

FAS8040*> df -g
Filesystem total used avail capacity Mounted on
/vol/vol0/ 285GB 14GB 270GB 5%    /vol/vol0/
/vol/vol0/.snapshot 15GB 0GB 14GB 2% /vol/vol0/.snapshot
/vol/vol1/ 100000GB 91607GB 8392GB 92%    /vol/vol1/
snap reserve 0GB 0GB 0GB 0% /vol/vol1/..
/vol/vol2/ 10000GB 11GB 9988GB    0%    /vol/vol2/

snap reserve 0GB 0GB 0GB 0% /vol/vol2/..

Please answer my question...

Thank you.

Re: Why is the capacity displayed differently on the server when configuring the volume?

NetApp_SR — Wed, 18 Mar 2020 01:31:41 GMT

Volumes may have Snap Reserve and other overhead. Please review below KBs.

Space Usage

https://kb.netapp.com/app/answers/answer_view/a_id/1001011

How is space utilization managed in a Data ONTAP SAN environment?
https://kb.netapp.com/app/answers/answer_view/a_id/1002502

Re: Why is the capacity displayed differently on the server when configuring the volume?

paul_stejskal — Wed, 18 Mar 2020 17:30:13 GMT

Which protocol? That makes a difference. If it's a LUN, you will always be looking at the file system the initiator puts on the LUN. When you look at ONTAP, you look at the WAFL file system in the FlexVol layer, or in the Aggregate. Those are 3 different things and each one will show a completely different amount of free and total space. There is typically a discrepancy between an initiator file system (NTFS, EXT4, VMFS, etc.) and a FlexVol or even the LUN size.

The reason why a LUN shows different is because it is a blob, and data may have been overwritten but not sent to be zeroed from the initiator (SCSI_UNMAP or TRIM). Rather than freeing the blocks, the LUN file in ONTAP just overwrites old blocks with new blocks as they are written if not in use anymore. The only way to get it to mostly match up is some kind of Space Reclamation or doing a zeroing operation. This is not normally recommended due to performance overhead, and must be scheduled.

I hope this helps.

If it's a NAS volume, there are a few things as mentioned in the prior post.