topic Re: How to return free block to aggr after de-dup without fractional reserve in ONTAP Discussions

How to return free block to aggr after de-dup without fractional reserve

martinthibert — Thu, 05 Jun 2025 07:27:00 GMT

On page 30 of the documentTR-3505-03-09 (Excellent technical doc btw), it's written that you have to configured your volume garantee at none, but when you configure a volume that way you are unable to change the fractional reserve to any other value then 100%.

vol options fc2_wind_page_ctx_dr fractional_reserve

vol options: Volume option fractional_reserve can be modified only if the volume has its guarantee option set to 'volume'.

Is there a way to configure to configure a volume, so the free block will be returnm to the aggr with fractional reserve = 0?

Right now I am using this config

volume garantee = volume

lun space reservation value = off

fractional reserve = 0

try_first - volume_grow

Once and awhile, i will downsize my volume.

Re: How to return free block to aggr after de-dup without fractional reserve

sajan — Fri, 19 Jun 2009 19:09:32 GMT

When volume garantee is set at none, fractional reserve is basically no op. In this case no physical storage is reserved and the reservation is effectively disabled. The configuration E mentioned in the TR3505 will be best one to get the free space in aggregate:

E: LUN CONFIGURATION FOR MAXIMUM AGGREGATE SPACE SAVINGS

In many cases, the user may prefer to reclaim all freed blocks from the Volume, and return these blocks to the aggregate free pool.

This is accomplished via the following configuration:

1) LUN Space Reservation value = Off

2) Volume Fractional Reserve value = any value from 0-100

3) Volume Guarantee = none

4) Snap Reserve = 0%

5) Autodelete = on

6) Autosize = on

7) Try_first = volume_grow

Re: How to return free block to aggr after de-dup without fractional reserve

martinthibert — Tue, 23 Jun 2009 15:07:18 GMT

Does the saved space will return automatically to the aggr after running a A-SIS or this is a manual process?

Re: How to return free block to aggr after de-dup without fractional reserve

danielmorgenstern — Tue, 23 Jun 2009 17:24:28 GMT

I believe that if the volume is thin provisioned (guarantee set to none), the blocks will be released back the aggregate.

If just the luns within the volume are thin provisioned ("space reserved" not set), the blocks will be freed within the volume but not released to aggregate free space.

edit: it's automatic if the guarantee is none and lun reservation turned off.

Re: How to return free block to aggr after de-dup without fractional reserve

sajan — Tue, 23 Jun 2009 17:32:55 GMT

The saved space will automatically return to the aggregate.

Re: How to return free block to aggr after de-dup without fractional reserve

jooss — Tue, 23 Jun 2009 17:40:36 GMT

> vol options: Volume option fractional_reserve can be modified only if the volume has its guarantee option set to 'volume'.

> Is there a way to configure to configure a volume, so the free block will be returnm to the aggr with fractional reserve = 0?

Currently, the fractional_reserve can only be set to 100% when guarantee=none. This will be changing in a future ONTAP release so that we can have guarantee=none and fractional_reserve=0%. As Sajan mentioned with a guarantee=none the fractional_reserve doesn't actual reserve physical space but we want to allow setting it to 0% in all cases since that is now our general best practice and it's easier from a managability aspect.

Re: How to return free block to aggr after de-dup without fractional reserve

amiller_1 — Fri, 26 Jun 2009 21:55:24 GMT

Given the need for thin provisioning (except in a VMware NFS environment), the biggest thing here in my mind is running Operations Manager and having it alert about free space/space changes (so you know when data is changing significantly and/or you're running out of space).