Hey there! Last month, I posted a blog announcing the support for MetroCluster clusters as SVM Migrate endpoints. My colleague, Jeff Steiner, has also shared some insights about SVM Migrate in specific use cases (here and here) . But I realized we haven’t really dived into what SVM Migrate is, and how it works. So, let's take a closer look at SVM Migrate and explore its capabilities.
What is SVM Migrate?
In the world of IT management, data mobility is a constant need. Whether you’re moving applications and their data for capacity balancing, performance optimization, technology updates, or disaster avoidance, the goal is to do it efficiently and without disruption. And that’s where SVM Migrate comes in.
NetApp has always offered a robust suite of data movement tools in ONTAP, with SnapMirror being one of the most well-known features. SnapMirror supports various recovery point objectives (RPO) and recovery time objectives (RTO) for data protection, often used for "forever incremental backups." But many also use SnapMirror as a data migration tool.
SVM Migrate, also known as SVM data mobility or vserver migrate, builds on the same proven data replication technologies pioneered by SnapMirror. SVM Migrate uses both asynchronous and synchronous replication engines to move data between ONTAP clusters while maintaining all the native ONTAP storage efficiencies like deduplication, compression, and compaction. It also ensures that any encryption on the data is preserved, keeping your data safe during the migration.
Why SVM Migrate?
SVM Migrate does exactly what its name suggests—it migrates entire storage virtual machines (SVMs), which are core data management structures within ONTAP, from one cluster to another. This includes not just the data volumes but also the SVM configuration information such as access control lists (ACLs) and NFS or SMB server settings. This ensures that client computers can continue to access the data using the same NAS export or share as before (Figure 1).
Figure 1: SVM Migrate overview
How SVM Migrate Works
SVM Migrate breaks the migration process into several phases (Figure 2):
- Initialize: This phase involves extensive prechecks on both the source and destination clusters to ensure the migration can be completed successfully. It checks for adequate space, compatible aggregate types, supported ONTAP versions, and the presence of any unsupported features. During this phase, the SVM and volume structures are created on the destination cluster, along with the SnapMirror asynchronous replication relationships and the SVM configuration migration relationship.
- Transfer: During this phase, the migrating SVM continues to operate in production while the data is asynchronously migrated by SnapMirror. The duration of this phase depends on the amount of data, ranging from minutes to days. The good news is that this process runs in the background, using excess bandwidth and CPU cycles, so there’s no impact on your production applications.
- Pre-cutover: This phase prepares for the actual migration cutover. The configuration of the source SVM is locked preventing any changes while the final configuration information is replicated one last time. Also during this phase, all traffic to the source volumes are paused and a final data replication takes place before converting the asynchronous data replication to a synchronous data replication.
- Cutover: Here’s where the magic happens. Once the synchronous replication relationship has started, SVM Migrate pauses all client traffic to the source volumes, turns off all data interfaces (data LIFs) on the SVM, and performs a failover to the destination cluster. Once the destination SVM is online, all data LIFs are brought up, and clients can start accessing data again at the new location. This phase takes less than 2 minutes, ensuring minimal disruption to your applications.
- Post-cutover: In the final phase, SVM Migrate cleans up the migration artifacts, removes snapshots from the source cluster, releases all replication relationships, and deletes the source SVM.
Figure 2: SVM Migrate performs multiple steps to migrate data
Flexibility to fit your operational needs
SVM Migrate offers several optional switches to address special scenarios. It also supports both the ONTAP command-line interface (CLI) or industry-standard REST API commands.
Table 1: SVM Migrate advanced options
|
Option |
Comments |
|
CLI: -check-only REST: “check_only”: <bool> |
• Perform all pre-migration checks • Provides list of items that would prevent successful migration • Default is false |
|
CLI: -auto-cutover REST: “auto_cutover”: <bool> |
• Enables a pause in the migration process at the point of actual cutover. • Default is true • Use vserver migrate cutover when ready to activate new SVM |
|
CLI: -throttle <KBps> REST: “throttle”: <integer> |
• Limit allowed bandwidth consumption on each intercluster LIF. • Values in kilobytes per second (KB/s) • Minimum value is 4KB/s (-throttle 4) • Default is unlimited (-throttle 0) |
|
CLI: -auto-source-cleanup REST: “auto_source_cleanup”: <bool> |
• Deletes source SVM and all volumes after migrate completes cutover to new cluster • Default is true • Use vserver migrate source-cleanup when ready to remove source SVM |
|
CLI: -aggr-list <aggr1>,<aggr2>,etc. REST: “destination.volume_placement.aggregates” <array aggregates> |
• Provide a list of aggregates that migrate can use to place volumes • Migrate determines all volume placement based on aggregate features and free capacity availability |
Check the full online command documentation for more details.
Limitations
While SVM Migrate is a powerful tool, there are some limitations to be aware of:
- Currently, it only supports NAS workloads. SAN support is under consideration for future updates.
- You can only perform one migration at a time, so plan accordingly if you need to migrate multiple SVMs.
- It supports FlexVol volumes only, not FlexGroup volumes or consistency groups.
Despite these limitations, SVM Migrate is continually evolving. We introduced it in ONTAP 9.10.1 and have been adding more support and features, including recent support for MetroCluster in 9.16.1. Stay tuned for more updates!
For more detailed information about SVM Migrate, please refer to SVM data mobility overview in the online NetApp ONTAP documentation.
SVM Migrate is a powerful tool to have in your data management arsenal. It provides an easy way to move SVMs between clusters based on your unique requirements without incurring any downtime for application that are dependent on the migrating data. As always, feel free to comment and ask any questions you might have.