What's different of Snapmirror configuration and SnapVault configuration?

[AllenChang]

When config Snapmirror and SnapVault,

the command is also use snapmirror,

but what's the major different parameter cause different effect ?

Thanks

[Ontapforrum]

SnapMirror is disaster recovery technology, designed for failover from primary storage to secondary storage at a geographically remote site. SnapVault is archiving technology designed for disk-to-disk Snapshot copy replication for standards compliance and other governance-related purposes.

There is plenty of documentation about the diferences on the NetApp knowledgebase and/or Internet.

https://kb.netapp.com/onprem/ontap/dp/SnapMirror/What_are_the_SnapMirror_policy_types_and_what_do_they_mean

More latest info (Policy types section):

https://www.netapp.com/pdf.html?item=/media/17229-tr4015pdf.pdf

[ansley_tj]

In the "old days," there was a technological difference between the replication engines used by SnapMirror using an async-mirror policy and SnapMirror using a vault policy, but that has changed such that both "SnapMirror" and "SnapVault" use the same replication engine. The only difference is in what each of those policies allows.  An async-mirror policy does not allow user-defined SnapMirror rules that tell SnapMirror which source Snapshot copies to replicate along with the "active" file system. A vault policy only backups up the source Snapshot copies, but does not continually update the source's "active" file system.  A mirror-vault policy allows both.

For all intents and purposes, "SnapVault" is simply "snapmirror with a vault policy".  

For more details, you can download TR-4015

[AllenChang]

Hi ansley_tj

Would you give me two example cli ?

one is for snapmirror and the other is  snapvault

Thanks

[ansley_tj · Accepted solution]

Technically, the only difference in the policy creation is the -type
parameter used to create the policy, but in reality, once you create the policy
a "vault" policy will also need one or more rules to replicate any desired source
snapshots. The number you keep on the destination doesn't really matter...you can keep the same number of snapshots on the destination as is kept on the source, or keep more more snapshots on the destination as is kept on the source.  It is still a vault policy.

For a VAULT policy:
1) create the base policy

Vs0.example.com::> snapmirror policy create -vserver vs0.example.com -policy MyVaultPolicy -type vault

vs0.example.com::> snapmirror policy add-rule -vserver vs0.example.com -policy MyVaultPolicy -snapmirror-label nightly -keep 5

Vs0.example.com::> snapmirror policy show -policy MyVaultPolicy

Vserver Policy Policy Number Transfer Name Name Type Of Rules Tries Priority Comment ------- ------------------ ------ -------- ----- -------- ----------

MyVaultPolicy         vault 2 8 normal Vault policy  SnapMirror Label: nightly                              Keep: 5

For a MIRROR policy:

A snapmirror policy will use -type async-mirror, which will have one rule by default...the "sm_created" rule:

Vs0.example.com::> snapmirror policy create -vserver vs0.example.com -policy MyAsyncMirrorPolicy -type async-mirror

Vs0.example.com::> snapmirror policy show -policy MyAsyncMirrorPolicy

Vserver Policy Policy Number Transfer Name Name Type Of Rules Tries Priority Comment ------- ------------------ ------ -------- ----- -------- ----------

MyAsyncMirrorPolicy async-mirror 1 8 normal Asynchronous SnapMirror policy for mirroring the latest active file system. SnapMirror Label: sm_created Keep: 1 Total Keep: 1

This tells snapmirror to only replicate the snapshot of the active file system it creates as part of the scheduled snapmirror replication. 

Notice that the Vault policy does not have a rule for "sm_created" and the AsyncMirror policy does not have any rules EXCEPT the "sm_created"

A couple of notes:

1. you can only keep one "sm_created"...you cannot change the keep value
2. you can add ONE additional rule to an async-mirror policy. That rule must be -snapmirror-label all_source_snapshots.  This will replicate all snapshots that are on the source regardless of label and still keep only one copy on the destination.

 A policy of -type mirror-vault allows both of the above in same policy.

The bottom line is that all three policies use the exact same replication engine to perform the replication...what changes is what the policy allows...vault has one or more custom rules, async-mirror has no custom rules, and mirror-vault has both.

All of this is explained in TR-4015. Also, the online MAN pages for  snapmirror policy create and snapmirror policy add-rule commands are available.

[AllenChang]

Thanks very much for your answer

[AllenChang]

if snapmirror policy rulle's Retention Count more than snapshot policy schedule count,it's the snapvault ?
if snapmirror policy rulle's Retention Count equal snapshot policy schedule count,it's the snapmirror ?

Is it right?

[ansley_tj]

Not necessarily. See my response to your previous message.