Administrator Guide

Live Volume support for Microsoft Windows/Hyper-V
82 Dell EMC SC Series: Synchronous Replication and Live Volume | CML1064
9.11 Live Volume with SQL Server
While SQL Server database files can be stored on Live Volumes, it is important to understand how a primary
volume failure can impact database availability. If a database cannot be recovered after a primary volume
failure, from either a frozen snapshot or the active snapshot on the secondary volume, a restore from backup
will be required. Recovering from backup can greatly increase the time it takes to recover from a failure of the
primary volume. If Live Volume is used across multiple sites, it is important to ensure that current database
backups are always available at the secondary site.
Replay Manager cannot be used to protect SQL Server data stored on Live Volumes. Snapshots on a Live
Volume will always be crash consistent. Unfortunately, database recovery from crash-consistent snapshots is
not always successful, especially when database files are spread across multiple volumes. While generally
not a best practice, placing all files for a given database on the same volume will increase the odds of a
successful recovery from crash-consistent snapshots.
As long as the primary and secondary volumes are synchronized, database recovery should be reliable from
the active snapshot on the secondary volume, if the primary volume fails. Since asynchronous Live Volume
does not keep the primary and secondary volumes synchronized, synchronous Live Volume should be used
for SQL Server database files. If synchronous Live Volume is used in high availability mode, the secondary
volume may not always be in sync with the primary. A successful recovery from the active snapshot on the
secondary volume may not be possible if it is out of sync. Synchronous Live Volume in high consistency
mode provides the best protection.
Live Volume with automatic failover can be used to create a multi-site failover cluster instance of SQL Server.
As long as the sites are synchronized, SQL Server will automatically bring the instance online at the
secondary site if the primary site were to fail. If Live Volume is set up in a uniform configuration, it is possible
for SQL Server to be running in one site and the primary volume in another. Using Live Volume in a non-
uniform configuration, where each node of the cluster only has volume mappings to the local array and with
automatic role swap enabled, will help ensure that SQL Server and the primary volume are running at the
same site. Since Live Volume with automatic failover uses synchronous replication in high availability mode,
the secondary volume is not guaranteed to always be in sync with the primary. If a failure occurs while the
secondary is out of sync, manual intervention will be required to recover the SQL Server instance.
If automatic failover is not needed, regular replication may be a better choice to protect SQL Server data.
Replication alone offers recovery times comparable to Live Volume without losing the protection benefits of
application-consistent snapshots provided by Replay Manager, reducing the risk of having to recover from
backup in the event of a failure. The entire recovery can be scripted using Microsoft PowerShell
®
, reducing
recovery time and minimizing mistakes.