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14 Dell EMC SC Series: Disaster Recovery for Microsoft SQL Server Using VMware Site Recovery Manager | CML1018
4 Solution design
SRM can be configured to use either vSphere Replication (VR) or array-based replication. This paper will only
cover using SRM with array-based replication, specifically SC Series replication. Before creating the recovery
plan in SRM, the type of replication, the method used to create snapshots, and the frequency for which
snapshots are taken need to be selected. For virtual machines running SQL Server, it is critical to create
snapshots that SRM can use to reliability recover databases. Replay Manager leverages VSS to provide the
application and data consistency that ensures consistent, reliable database recovery. Once a replication and
snapshot strategy is chosen, DSM and SRM can be configured to facilitate a failover that meets the RPO and
RTO requirements.
4.1 Choosing a snapshot strategy
When creating snapshots for volumes containing SQL Server data, it is recommended to use Replay
Manager. This provides the most reliable snapshots from which to recover SQL Server data. Replay Manager
leverages the VSS to ensure application consistency. If Replay Manager cannot be used, it is highly
recommended to use a consistency group when protecting SQL Server data stored across multiple volumes.
Regardless of the method used to create snapshots, be sure to take snapshots often enough to meet RPO
requirements. For example, if the RPO is 60 minutes, snapshots should be taken at least every 60 minutes. If
the link between sites is slow or unreliable, snapshots might need to be taken more often.
The recovery of virtual machines by SRM can vary depending on the method used to create snapshots. When
choosing a snapshot mechanism, be sure to consider the recovery implications. To help simplify the recovery
process, choose the same snapshot mechanism for all snapshots on a given volume. PowerShell scripts
written to automate a recovery plan will be less complex if they do not have to determine the type of snapshot
used for the recovery.
4.1.1 Using Replay Manager with .VMDKs
Either one of the VMware backup extensions can be used to create application consistent snapshots of SQL
Server data stored on .vmdks. Consider the following when using Replay Manager with .vmdks:
• When using either VMware extension:
- If a virtual SCSI controller hosts more than 7 virtual disks in a virtual machine, vSphere snapshots
will work, but it will not provide application consistency.
- The vSphere snapshot will fail if any VSS-aware application data, like a SQL Server database,
are stored on a disk type other than a .vmdk or a vRDM.
• When using the VMware Datastores extension:
- Ensure all datastores used by protected SQL Server instances are included in the backup set.
- If the vSphere snapshot for one or more virtual machines fails, the job will still succeed.
• When using the VMware Virtual Machines extension:
- Select the SQL Server virtual machines for the backup set. Replay Manager will automatically
build a list of volumes to include based on the VMs selected.
- If the vSphere snapshot for one or more virtual machines fails, the entire job fails.