Resize limits for SAN LUNs

If you run lun resize command on NetApp you might run into the following error:

lun resize: New size exceeds this LUN’s initial geometry

The reason behind it is that each SAN LUN has head/cylinder/sector geometry. It’s not an actual physical mapping to the underlying disks and has no meaning these days. It’s simply a SCSI protocol artifact. But it imposes limitation on maximum LUN resize. Geometry is chosen at initial LUN creation and cannot be changed. Roughly you can resize the LUN to the size, which is 10 times bigger than the size at the time of creation. For example, the 50GB LUN can be extended to the maximum of 502GB. See the table below for the maximum sizes:

Initial Size   Maximum Sizedata-storage
< 50g          502g
51-100g        1004g
101-150g       1506g
151-200g       2008g
201-251g       2510g
252-301g       3012g
302-351g       3514g
352-401g       4016g

To check the maximum size for particular LUN use the following commands:

> priv set diag
> lun gemetry lun_path
> priv set

If you run into this issue, unfortunately you will need to create a new LUN, copy all the data using robocopy for example and make a cutover. Because such features as volume level SnapMirror or ndmpcopy will recreate the LUN’s geometry together with the data.

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