Planning for upgrading storage systems running SnapMirror

Upgrade requirements for SnapMirror

If you are upgrading Data ONTAP on storage systems that are running the SnapMirror® software, you must upgrade the systems that have SnapMirror destination volumes before you upgrade the systems that have SnapMirror source volumes. For SnapMirror volume replication, the destination volume must run under a version of Data ONTAP equal to or later than that of the SnapMirror source volume.

Note
This requirement applies to both asynchronous and synchronous SnapMirror for volume replication.

The requirement does not apply to SnapMirror for qtree replication, SnapVault, or data restoration from tape using the restore command. However, make sure that when you upgrade systems that use these features, you should upgrade your SnapMirror destination systems, SnapVault® secondary systems and restoration target systems before the corresponding source systems to maintain backward compatibility.

To upgrade asynchronous or synchronous SnapMirror for volume replication, use the following process.

Stage	Description
1	Identify any destination volumes.
2	Upgrade the storage systems with destination volumes, beginning with the furthest one in the topology (that is, the last system in a series of cascading destinations).
3	Upgrade the storage system with the source volume.

The following sections provide more detail about:

Identifying SnapMirror destination volumes
Upgrading storage systems running synchronous SnapMirror
Why you must plan for SnapMirror upgrades
Upgrading storage systems that are mirroring volumes to each other
For more information
Attention
You must upgrade the storage systems that have SnapMirror destination volumes before upgrading those that have source volumes. If you upgrade the source volumes first, SnapMirror volume replication is disabled. To re-enable SnapMirror volume replication, you must downgrade the source system or upgrade the destination system, so that the version of Data ONTAP on the source system is earlier or the same as that on the destination system.

Identifying SnapMirror destination volumes

SnapMirror source volumes can be replicated to single or multiple destination volumes. (Replication to multiple destination volumes is also referred to as replication to cascading destinations.) When you upgrade Data ONTAP, you must identify all destination volumes and then upgrade the storage systems on which they reside before upgrading the system where the source volume resides. In addition, when you upgrade storage systems in a cascading series, you should upgrade the systems in order, beginning with the destination systems furthest in your topology from the source system.

Note
Upgrading to Data ONTAP 7.0 or later preserves volumes created with earlier release families as traditional volumes. With the Data ONTAP 7.0 release family, you can also create FlexVol^TM volumes. When running SnapMirror software, the source and destination volumes must be of the same type, either traditional or flexible. For information about traditional and FlexVol volumes, see the Storage Management Guide and About volume types after upgrading to Data ONTAP 7.0 or later in this guide.

To identify storage systems with SnapMirror destination volumes, complete the following step.

Step	Action
1	On the storage system with the source volume, enter the following command: snapmirror destinations Result The `snapmirror` command lists all destination volumes, including cascaded destinations. For more information about the `snapmirror` command and options, see the snapmirror(1) man page.

Upgrading storage systems running synchronous SnapMirror

Use the same process to upgrade storage systems running synchronous SnapMirror as described in Upgrade requirements for SnapMirror.

However, synchronous SnapMirror requires that the source and destination run the same version of Data ONTAP. Hence, when you upgrade a destination storage system in a synchronous mirror, SnapMirror goes into asynchronous mode. When in asynchronous mode, the source system asynchronously replicates data to the destination every minute until a synchronous replication can be reestablished; that is, until the source system is upgraded so that the same Data ONTAP version is running on destination and source systems.

Why you must plan for SnapMirror upgrades

When you upgrade Data ONTAP on storage systems that have a mirrored relationship with each other using SnapMirror, the order in which you upgrade the storage systems is critical. If you do not upgrade in the correct order, you can cause a lapse in SnapMirror replication coverage.

A SnapMirror transfer is initiated when the destination storage system reads a Snapshot^TM copy of the source system. Therefore, the destination system must be upgraded first, so that it can read the snapshots of the earlier release. If the source system is upgraded first, the destination system cannot read the source system's file system, thereby disabling SnapMirror.

Upgrading storage systems that are mirroring volumes to each other

SnapMirror can be configured to enable two storage systems to mirror each other's volumes. In this case, each storage system is both a source and a destination system. For example, System A can mirror volumes to System B, and System B can mirror volumes to System A.

In this configuration, there is logically no way to update both destinations before the corresponding source systems. Therefore, to upgrade Data ONTAP on storage systems that are mirroring volumes to each other, you must disable the mirror, upgrade each system, and reenable the mirror.

For more information

For more information about running SnapMirror, see the Data Protection Online Backup and Recovery Guide.