What is SnapMirror active sync?
SnapMirror active sync, formerly known as SnapMirror Business Continuity, provides a business continuity solution for business-critical applications hosted on the ONTAP platform and data are synchronously replicated across the failure domain. SnapMirror active sync is easy to implement and provides flexibility for application-level granularity for automatic failover.
SnapMirror active sync uses SnapMirror synchronous replication technology along with consistency groups for dependent write-order consistency when there are multiple volumes involved. In the event of a site failure, SnapMirror active sync enables your application services to continue from a secondary replica with transparent failover. No manual intervention nor additional scripting is required in this process.
SnapMirror active sync feature can be integrated seamlessly with critical infrastructure services such as VMware vSphere, and enterprise databases such as Microsoft SQL Server and Oracle in both virtual and physical environments. SnapMirror active sync (formerly SnapMirror Business Continuity) is supported from ONTAP 9.8 and until ONTAP 9.13.1, it would work for the standalone setup of SQL Server but not for the SQL Server Always on Failover Cluster instance because of its limitation on SCSI-3 Persistent Reservation.
During the Microsoft Windows server failover cluster setup, you would run the cluster validation test to verify the storage support and SCSI commands that are required by clustering services. If SCSI-3 Persistent Reservation(PR) is not supported then you would run into the error as shown below --
What's new in ONTAP 9.14.1
Before mentioning what’s new in ONTAP 9.14.1 for SnapMirror active sync let me explain what is SCSI-3 persistent reservation.
SCSI reservations are used to control access to a shared SCSI device such as a disk. An initiator sets a reservation on a LUN to prevent another initiator from making changes to the LUN. This is similar to the file-locking concept. SCSI reservations are always set by a host initiator. Ideally, the same initiator would perform a SCSI release on the affected LUN. The mechanics of SCSI reservations are specified in the SCSI protocols. SCSI-3 Primary Commands specification provides a modern approach to reservations known as Persistent Reservations. Persistent Reservations add the ability for the reservation to persist even if the bus is reset for error recovery or node reboots. A PR is an SCSI command that clustering uses to protect LUNs. When a LUN is reserved, no other computers on the SAN can access the disk, except the ones cluster controls. This is important to protect other machines from accessing the disk and corrupting the data on the disk.
Windows failover cluster requires SCSI-3 PR command to manage ownership of clustered disk on a node. Since clustered disks are shared across the nodes, only one node can access the data at any time to avoid corruption of the data on the LUN, when one node has the ownership then that node would place a reservation on that disk and if another node tries to access it, It would request for ownership which could either be granted or denied & secondary node is granted ownership during the failover process.
ONTAP 9.14.1 adds support to SnapMirror active sync for SCSI-3 persistent reservation. With this capability, you can design disaster recovery for critical SQL Server database running on Windows server failover cluster setup. Here is the screenshot of the successful validation for SCSI-3 persistent reservation during the Windows server failover setup.
SnapMirror active sync supportability for SCSI-3 Persistent Reservation
- SCSI-3 Persistent Reservation (PR) is supported on Windows Failover Clustering with SnapMirror Business Continuity (SM-BC) starting from ONTAP 9.14.1 and onwards.
- Windows Failover Cluster (SCSI-3 PR) on vSphere ESXi GOS is supported with SnapMirror Business Continuity (SM-BC) starting from ONTAP 9.14.1 and onwards.
- Hyper-V Cluster configured on Windows Failover Cluster with SCSI-3 PR is supported with SnapMirror Business Continuity (SM-BC) starting from ONTAP 9.14.1 and onwards.
- Other host cluster solutions using SCSI-3 PR across other Operating Systems are not supported.
Please refer the NetApp Interoperability Matrix Tool (IMT) for latest configuration compatibility.
Conclusion
Strategizing high availability or disaster recovery is always crucial for any mission critical applications. NetApp ONTAP SnapMirror active sync can help to provide the desired outcome with minimal disruption to your databases hosted on SAN using iSCSI or FC-based protocol across the sites to create robust business continuity solutions.
Databases can continue to run in event of storage failover without needing to restart database services thus achieving near zero recovery time objective along with recovery point objective for databases running on standalone instances or failover clustered instances.
Check out more about SnapMirror active sync from ONTAP documentation.
