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Overview of Dell EMC SC Series tools for HA/DR
5 SQL Server High Availability and Disaster Recovery with Dell EMC SC Series | CML1119
1 Overview of Dell EMC SC Series tools for HA/DR
Several types of events can have an effect on the availability of SQL Server databases and the applications
that use them. These events range from unplanned events, such as natural disasters that may impact an
entire data center, to planned events such as hardware or software upgrades. Dell EMC SC Series arrays
have several features that enable customers to deploy architectures that are resilient to these types of events
and increase the overall availability of SQL Server databases. This section gives a brief overview of each
feature, as well as best practices and use cases when implementing these features in SQL Server
environments.
1.1 Snapshots
One of the fundamental features that SC Series arrays provide is the ability to perform storage-based
snapshots at the volume level. Since snapshots are a metadata operation, they allow a recovery point to be
created in seconds, no matter how large the volume, while requiring minimal space. The speed and space
efficiency of array-based snapshots simply cannot be matched by traditional protection methods. This unique
capability is the building block for other SC Series availability and protection features.
When the boot volume is also hosted on the array, the entire server can be protected with snapshots. This is
extremely useful when patching systems and/or performing software upgrades. The system can to be quickly
reverted to its prior state if something goes wrong. Typically, full system backups would take many minutes or
even hours to create and a similar duration to restore. Since reverting the system from snapshots simply
involves metadata operations and volume remapping, the entire recovery process can be completed in a
fraction of the time, minimizing downtime for critical applications.
1.2 Replay Manager
Replay Manager is the recommended way to take snapshots of SQL Server database volumes. Replay
Manager is an application that creates and manages application consistent snapshots on an SC Series array.
Application consistency is provided using the Microsoft Volume Shadow Copy Service (VSS). The Replay
Manager VSS provider, along with VSS communicate between SQL Server and the SC Series array to
ensure application consistency. This provides reliable SQL Server database recovery from snapshots that can
be used for same server recovery, recovery on a different server, or recovery from a different array.
While snapshots can be taken on the array without Replay Manager, SQL Server is not aware of snapshots
taken without Replay Manager and in-flight data that has not been written to storage will be excluded from the
snapshot. Using Replay Manager ensures that data is flushed to disk and writes are held before taking a
snapshot.
Replay Manager provides several recovery options that simplify the process of snapshot-based database
recovery. When recovering databases on the original server, Replay Manager restore points can be used with
SQL Server log backups to perform point-in-time recovery, using either the Restore or Resync method. The
Resync method provides an extremely fast way to recover a large SQL Server database without taking the
time required by a full database restore from traditional backups. The Expose feature in Replay Manager can
also be used to perform a side by side recovery of a database for scenarios where object-level recovery or
further data analysis is needed. The Using Replay Manager with Microsoft SQL Server video presents an
excellent overview of Replay Manager functionality. For a complete description of Replay Manager features,
consult the Replay Manager Administrators Guide. There are also several videos and white papers on SC
Series technical documents that cover Replay Manager features and recovery scenarios in detail.