Ontap revert from 9.2 to 9.1, NDU?

[smysq2]

We having to downgrade (revert) Ontap on a 2 node Cluster to bring it in line with the rest of our environment. We cannot upgrade due to hardware type limited to Ontap 9.1 (FAS3250s), so for now we need to downgrade the FAS8200s to allow us to SnapMirror.

I've read through the Upgrade and Revert/Downgrade Guide (link below) and I have a few concerns.

https://library.netapp.com/ecm/ecm_download_file/ecmlp2492712

Query 1) Is the revert non-disruptive (like an upgrade)? in the linked document Page 85 it states:

"You need to consider the revert issues and limitations before beginning an ONTAP reversion.
• Reversion is disruptive.
No client access can occur during the reversion. If you are reverting a production cluster, be sure
to include this disruption in your planning.
• Reversion affects all nodes in the cluster.
The reversion affects all nodes in the cluster; however, the reversion must be performed and
completed on each HA pair before other HA pairs are reverted"

Query 2) Is it necessary for me to decompress my SE volumes and disable dedup? Page 92-92 states it is!

"Reverting from ONTAP 9 on a system that has deduplication enabled includes running advanced
mode commands. You must contact technical support for assistance.
If you have enabled both deduplication and data compression on a volume that you want to revert,
then you must revert data compression before reverting deduplication."

Query 3) Do I need to suspend all my snapshot policies and delete snapshots prior to current release? See page 94:

"Before reverting to an earlier ONTAP release, you must disable all Snapshot copy policies and delete
any Snapshot copies that were created after upgrading to the current release."

I'm hoping I'm simply misunderstanding the instructions as the Upgrade Advisor report I’ve ran isn’t suggesting such a disruptive method.

[christsai]

Hi @smysq2 

If the downgrade reason is for the snapmirror version dependence, maybe you can consider using Unified replication, Unified replication relationships allow you snapmirror between ONTAP 9.1 and 9.2 , then you can keep FAS8200 in 9.2.

https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.pow-dap%2FGUID-0810D764-4CEA-4683-8280-032433B1886B.html

[SpindleNinja]

I would skip the revert and switch everything to version flexable XDP snapmirrors.    See the chart at the bottom. 

https://docs.netapp.com/ontap-9/index.jsp?topic=%2Fcom.netapp.doc.pow-dap%2FGUID-0810D764-4CEA-4683-8280-032433B1886B.html

[smysq2]

Thanks, yes, this does work as I have set this up for some of our services but the idea is to standardise our Environment to 9.1. 

Would like to know if the process is as intrusive as the doc states.

[SpindleNinja · Accepted solution]

It can be.  I don't think it's worth the effort.  Reverts are generally meant for an emergency post codeupdate when stuff went "bad". 

one of the reasons XDP was developed and made standard in later version is so people can continue to operate with mix generation gear. 

[smysq2]

You're right - It's not worth the effort when XDP works - Thanks both!!