Thursday, 25 July 2019

Making a SnapMirror Vault Tertiary Copy, Read-Write and Primary: Part 1 of 2: Setting the Scenario

A bit of a random scenario here, but it showcases the flexibility and power of ONTAP.

I have 3 clusters*:

- Prod cluster (SVMA) has the Prod volume VOL001 with 7 daily snapshots, 8 weekly snapshots**
- DR cluster (SVMB) has the DR volume VOL001_DR and MirrorAllSnapshots from VOL001
- SV cluster (SVMC) has the Vault volume VOL001_SV and keeps 104 weekly snapshots

*In the lab below, I have just one cluster with 3 x SVMs, which is fine to prove the point.
**In the real world we’d have hourly’s or even better RPO, but for the sake of this scenario, 2 types of snapshot are fine. In the lab my daily snapshots are 1min snapshots, and weekly snapshots are 7min snapshots (can’t wait 2 years for the lab retention to build up.)

What I want is to have:

- Prod cluster (SVMA) with a new Prod volume VOL001_NEW (we’ll rename it back to VOL001) with 7 daily and 104 weekly snapshots
- DR cluster (SVMB) has the DR volume VOL001_DR with 7 daily and 8 weekly snapshots
- SV cluster is going

To make this easier to understand, here are some diagrams.

Image: Legend

Image: Current layout

Step 1: MirrorAllSnapshots to Prod New volume

Step 2: Modify the Vault SnapMirror Policy so it has all the source snapshots and will bring over a pre_cutover snapshot

Step 3: Halt client access to the volume in question, and take a pre_cutover snapshot that is replicated everywhere

Step 4: Tidy up the snapmirror relationship 1) DR, 2) Vault, 3) Prod New

Step 5: After renaming and remounting Prod New volume, resync it to DR

Step 6: Finally, we will tidy up the pre_cutover snapshot

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