A common use case for writable snapshots is in disaster recovery testing. For DR purposes, an enterprise typically has two PowerScale clusters configured in a source/target SyncIQ replication relationship. Many organizations have a requirement to conduct periodic DR tests to verify the functionality of their processes and tools in the event of a business continuity interruption or disaster recovery event.

Figure 6.   Writable snapshots and SyncIQ DR test workflow

Given the writable snapshots compatibility with SyncIQ caveats described in the previous table, a writable snapshot of a production dataset replicated to a target DR cluster can be created as follows:

1. On the source cluster, create a SyncIQ policy to replicate the source directory (/ifs/test/head) to the target cluster:

# isi sync policies create --name=ro-head sync --source-rootpath=/ifs/prod/head --target-host=10.224.127.5 --targetpath=/ifs/test/ro-head

# isi sync policies list

Name  Path              Action  Enabled  Target

---------------------------------------------------

ro-head /ifs/prod/head  sync    Yes      10.224.127.5

---------------------------------------------------

Total: 1

2. Run the SyncIQ policy to replicate the source directory to /ifs/test/ro-head on the target cluster:

# isi sync jobs start ro-head --source-snapshot s14

# isi sync jobs list

Policy Name  ID   State   Action  Duration

-------------------------------------------

ro-head        1    running run     22s

-------------------------------------------

Total: 1

# isi sync jobs view ro-head

Policy Name: ro-head

         ID: 1

      State: running

     Action: run

   Duration: 47s

 Start Time: 2021-06-22T20:30:53

Target:

3. Take a read-only snapshot of the replicated dataset on the target cluster:

# isi snapshot snapshots create /ifs/test/ro-head

# isi snapshot snapshots list

ID   Name                                        Path

-----------------------------------------------------------------

2    SIQ_HAL_ro-head_2021-07-22_20-23-initial /ifs/test/ro-head

3    SIQ_HAL_ro-head                          /ifs/test/ro-head

5    SIQ_HAL_ro-head_2021-07-22_20-25         /ifs/test/ro-head

8    SIQ-Failover-ro-head-2021-07-22_20-26-17 /ifs/test/ro-head

9    s106976           /ifs/test/ro-head

-----------------------------------------------------------------

4. Using the (non SIQ_*) snapshot of the replicated dataset above as the source, create a writable snapshot on the target cluster at /ifs/test/head:

# isi snapshot writable create s106976 /ifs/test/head

5. Confirm the writable snapshot has been created on the target cluster:

# isi snapshot writable list

Path              Src Path         Src Snapshot

----------------------------------------------------------------------

/ifs/test/head  /ifs/test/ro-head  s106976

----------------------------------------------------------------------

Total: 1

# du -sh /ifs/test/ro-head

 21M    /ifs/test/ro-head

6. Export or share the writable snapshot data under /ifs/test/head on the target cluster using the protocol or protocols of choice. Mount the export or share on the client systems and perform DR testing and verification as appropriate.
7. When DR testing is complete, delete the writable snapshot on the target cluster:

# isi snapshot writable delete /ifs/test/head

Writable snapshots cannot be refreshed from a newer read-only source snapshot. A new writable snapshot would need to be created using the newer snapshot source in order to reflect and subsequent updates to the production dataset on the target cluster.

More information about OneFS SyncIQ replication configuration and management is available in the SyncIQ best practices guide.