Volume and Lun size

[saranraj456]

Hello Everbody,

I am been skeptical about the relationship between defining volume and LUN size for a quiet long time.

In our concern, we always used to create a volume 1 % higher than the LUN size.What was the use to create a volume in a such a way?

If in case we created a volume and Lun with same size whether it would create any problem? Please clarify.

Thanks,

Saran

[scottgelb]

There is some metadata so we like to keep at least 5-10% free in any container... so a volume 5-10% less than the volume size than the lun and at least 5-10% aggregate free space.. not always possible but good to have some wiggle room...leaves 10-20% free when keeping the aggr and volume with 5-10% each.

[scottgelb]

The Block Access Management Guide for iSCSI and FC (bsag.pdf in the ONTAP documentation) gives a clearer answer... that if you don't have snapshots then the lun can be the size of the volume.  I tend to be more conservative but without snaps it states it is ok.

http://now.netapp.com/NOW/knowledge/docs/ontap/rel801/html/ontap/bsag/GUID-35B62404-7D9B-4163-B43E-A5CDD9DDB399.html

     If you are not using Snapshot copies, the size of your volume depends on the size of the LUNs...

     The FlexVol volume should be at least as large as the size of the data to be contained by the volume.

     Example

     If you need a traditional volume to contain two 200-GB LUNs, you should create the volume with enough disks to provide at least 400 GB of storage capacity.