Accepted Solution

Reduce LUN size

Hi All

I need to reduce size of LUNs which are on windows 2008 servers to reclaim unused space. Could someone help me with the complete process to accomplish the task.


Re: Reduce LUN size

Could you give me some more information.. like whether the LUN is a thinly provisioned one or not; whether it is a iSCSI LUN for FC LUN; and some more details about your environment rather than just Windows 2008

In general...

Are you trying to reduce LUN size from you Windows box?

Then shrink your volume from first using disk management in Windows and  then reduce the size of LUN from the storage system.

Are you trying to reclaim the free space from a NTFS formatted thinly provisioned LUN?

Then the best way to do that would be using NetApp SnapDrive software...

Re: Reduce LUN size

The LUN is with space guarantee and it is FC LUN, following is the volume property containing the LUN,















We do not have snap drive licensed, I am looking to shrink the LUN on Netapp end.  I am also looking to clone the LUN as a fall back plan.

Is this the right way or is there a better way to accomplish it?

Re: Reduce LUN size

If you shrink you LUN on NetApp side without adjusting filesystem size you destroy your filesystem.

Re: Reduce LUN size

The first thing to do is to shrink partition on the OS side - unless it is already smaller than the LUN size (it can be seen via Disk Manager).

This is the procedure of shrinking Windows 2008 partition if we are talking about basic volume:



Re: Reduce LUN size

Okay, my first case applies to you. As myself and Radek have mentioned, you have to first shrink the partition from host side then resize the LUN accordingly from the storage.

Your backup plan is good. Create a snapshot of the volume that contains the particular LUN. Then do your things and once you verify everything is working as it should be, you can delete the snapshot that you created manually.

Re: Reduce LUN size

Thank you all for your response

What if I unmap the LUN, shrink the LUN and map it back again, will that also cause filesystem corruption.

Could you also breif me on the second method, reclaiming space from NTFS formatted thinly provisioned LUN.


Re: Reduce LUN size

Yes, it will cause filesystem corruption. You will cut off part of filesystem, possibly containing data.

Re: Reduce LUN size

Thanks all

final few questions

1) NTFS does not allow to shrink the volume by more than 50%, If I were to reduce it by more than 50% can I do it in 2 step  for eg:

If I have a 100 GB LUN, and on the OS side only 10 GB is used. can I

  • I shrink the volume to 50 GB  on the OS, take the volume offline, unmap the LUN and shrink the LUN to 50 GB.

  • Remap the LUN (now 50 GB) and shrink the volume size to 30 GB on the OS, offline the volume, umnap the LUN and shrink the LUN to 30 GB.

2) After shrinking the volume, how does Netapp ensures it does not cut off part of filesystem?


Re: Reduce LUN size

NetApp knows nothing about file system inside LUN. It is your responsibility to calculate new LUN size which will not damage file system. NetApp will not prevent you from setting LUN size to any value.