topic Re: Disk usage report greater than effective lun size in ONTAP Discussions

Disk usage report greater than effective lun size

NEXYLAN_ROUBAIX — Thu, 05 Jun 2025 06:34:29 GMT

Good morning everyone,

I'm having a weird issue with my FAS2020 running OnTap 7.3.6.

My volume 1 is 1,35TB.

System is reporting than this volume has only 221GB available (1116 MB used).

The thing is, I only have 2 lun created on this volume (200 + 500 GB). Snapshots are using 40 GB. Total : ~750GB used.

So, I was wondering where are the missing ~400GB ?

Am I missing something?

Thanks for your help,

GAëtan

Re: Disk usage report greater than effective lun size

NEXYLAN_ROUBAIX — Fri, 17 Feb 2012 09:06:07 GMT

fs1101> df -h

Filesystem total used avail capacity Mounted on

/vol/vol0/ 8755MB 640MB 8114MB 7% /vol/vol0/

/vol/vol0/.snapshot 460MB 152MB 308MB 33% /vol/vol0/.snapshot

/vol/vol1/ 1382GB 1161GB 220GB 84% /vol/vol1/

/vol/vol1/.snapshot 153GB 43GB 110GB 28% /vol/vol1/.snapshot

fs1101> df -Ah

Aggregate total used avail capacity

aggr1 2093GB 1555GB 538GB 74%

aggr1/.snapshot 110GB 87GB 22GB 79%

fs1101> aggr show_space -h

Aggregate 'aggr1'

Total space WAFL reserve Snap reserve Usable space BSR NVLOG A-SIS

2449GB 244GB 110GB 2093GB 0KB 0KB

Space allocated to volumes in the aggregate

Volume Allocated Used Guarantee

vol0 10GB 887MB volume

vol1 1544GB 520GB volume

Aggregate Allocated Used Avail

Total space 1555GB 521GB 538GB

Snap reserve 110GB 87GB 22GB

WAFL reserve 244GB 24GB 220GB

fs1101> aggr status

Aggr State Status Options

aggr1 online raid4, aggr root

fs1101> vol status

Volume State Status Options

vol0 online raid4, flex root, create_ucode=on

vol1 online raid4, flex no_atime_update=on,

create_ucode=on

Re: Disk usage report greater than effective lun size

aborzenkov — Sat, 18 Feb 2012 03:26:59 GMT

Which volume is it (vol0 or vol1)?

I asked for “df -r” output which you did not show.

Re: Disk usage report greater than effective lun size

aborzenkov — Sat, 18 Feb 2012 03:29:23 GMT

Please show output of “df -rh” for this volume.

Re: Disk usage report greater than effective lun size

NEXYLAN_ROUBAIX — Sat, 18 Feb 2012 09:17:42 GMT

Hello aborzenkov,

This is vol1.

Output of df -rh :

fs1101> df -rh

Filesystem total used avail reserved Mounted on

/vol/vol0/ 8755MB 640MB 8114MB 0MB /vol/vol0/

/vol/vol0/.snapshot 460MB 153MB 307MB 0MB /vol/vol0/.snapshot

/vol/vol1/ 1536GB 1217GB 318GB 463GB /vol/vol1/

/vol/vol1/.snapshot 0GB 51GB 0GB 0GB /vol/vol1/.snapshot

Yesterday, I changed reserved snapshot space to 0%. But no luck.

Gaëtan

Re: Disk usage report greater than effective lun size

aborzenkov — Sat, 18 Feb 2012 09:41:56 GMT

463GB is reserved for LUN overwrites due to fractional_reserve volume setting. This is done to protect you from out-of-space condition on LUNs. Please, read TR-3483 (or TR-3965 that includes 8.1) that describes in details how NetApp manages space in case of LUN.

Re: Disk usage report greater than effective lun size

NEXYLAN_ROUBAIX — Sat, 18 Feb 2012 10:13:36 GMT

Thanks for the tip aborzenkov !

What happens if I disable "Space Reserved" for this lun. What could happen?

Gaëtan

Re: Disk usage report greater than effective lun size

aborzenkov — Sat, 18 Feb 2012 12:34:51 GMT

You may run out of space on the volume, so that host write to LUN fails. As hosts normally do not expect hard disks to run out of space, they do not handle it gracefully.

Default settings on NetApp ensure, that there is always space for new write to LUN, so it behaves exactly as conventional disk.

Re: Disk usage report greater than effective lun size

NEXYLAN_ROUBAIX — Sat, 18 Feb 2012 13:03:10 GMT

What I don't understand is, why would a host require to write beyond my lun configured limit?

I created a 500GB lun on vol1 which is used by XenServer. XenServer know it has 500 GB available and not more.

In what case(s) would the "space reserve" be used?

Thanks,

Gaëtan

Re: Disk usage report greater than effective lun size

aborzenkov — Sat, 18 Feb 2012 13:09:42 GMT

Have you read TR-3483?