topic Re: how much extra space in a volume to store LUNs in ONTAP Discussions

how much extra space in a volume to store LUNs

SMASHINGPUMPKIN — Thu, 05 Jun 2025 06:11:10 GMT

We create 1 volume per server in our environment.
Netapp does not allow using all capacity in the volume,
so you always have to make the volume a bit larger than the LUN(s) stored in it.

My question is:
what is the minimum amount of free space in a volume that should be guaranteed when using the volume to store LUNs ?

EXAMPLE

volume - 101GB
LUN1: 50GB
LUN2: 50GB

We will not create snapshots of the volume.

volume settings:
-> NO SNAPSHOT SCHEDULES
-> NO SNAPSHOT RESERVE
-> SNAPSHOT AUTODELETE ENABLED, AUTOGROW DISABLED
-> NO fractional reserve
-> storage efficiency not enabled

The 2 LUNs are online and working,
but the volume is showing as 100% used.

The key question:
Is this safe (only 1GB extra in the volume),
or would it be safer to make the volume for example 110 GB ?

We don't unnecessarily want to waste space,
but we also don't want to run into a LUN offline condition.
Seeing the 100% used on the volume kinda makes me feel uncomfortable.

Re: how much extra space in a volume to store LUNs

radek_kubka — Wed, 30 Jan 2013 16:12:24 GMT

Hi,

It looks nasty (volume 100% full), but does work

If you want to change it by making the volume bigger & not waste space in the aggregate, why not set the volume guarantee to none?

Regards,

Radek

Re: how much extra space in a volume to store LUNs

ismopuuronen — Sat, 02 Feb 2013 18:56:07 GMT

Hello,

My question is:

what is the minimum amount of free space in a volume that should be guaranteed when using the volume to store LUNs ?

If you are able to create the LUNs and those are online & mapped, it's ok.

We will not create snapshots of the volume.

volume settings:

-> NO SNAPSHOT SCHEDULES

-> NO SNAPSHOT RESERVE

-> SNAPSHOT AUTODELETE ENABLED, AUTOGROW DISABLED

-> NO fractional reserve

-> storage efficiency not enabled

Are you doing any backups from the LUNs/volume?

The 2 LUNs are online and working,

but the volume is showing as 100% used.

Volume is showing 100% full, because LUNs are just a files for netapp. ONTAP doesen't know whats happening inside those files.

The key question:

Is this safe (only 1GB extra in the volume),

or would it be safer to make the volume for example 110 GB ?

If you aren't doing any snapshots from the volume, then the minimum amount of extra space needed to the volume is ok.
I'm pretty sure, ONTAP doesen't allow you to do too big LUN inside a volume.

We don't unnecessarily want to waste space,

but we also don't want to run into a LUN offline condition.

Seeing the 100% used on the volume kinda makes me feel uncomfortable.

If you don't do any snapshots from that volume you are safe.

LUN will not go to offline, until there isn't any problems in the aggregate, or above that.

I would put volume gurantee = volume, so it makes sure that the 0.xxGB is always available from the aggr (not sure, is it already), even tough fractional reserve would be 0%.

Situation where LUN can go to offline is example where the host sees that LUN is having free space, but volume isn't having that:

100GB volume having 99.xxGB LUN in it.

Host fills the the LUN totally -> snapshot occurs -> host deletes all the data inside the LUN.

This is the situation, where all the blocks inside the volume are locked by a snapshot.

Host sees the disk as a empty, but every write attempts will fail because there isn't room enough in the volume, and during write operation LUN could go to offline.

For avoiding these situations, we can use fractional space reserve, and for making sure snapshots are doing well also, we can add some snap reserve for the volume.

Br.

Ismo.