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Overview of Dell EMC SC Series tools for HA/DR
6 SQL Server High Availability and Disaster Recovery with Dell EMC SC Series | CML1119
1.3 Live Migration
Occasionally, there is a need to migrate storage between SC Series arrays for hardware refreshes, change of
location, or other reasons. Typically, this would involve replicating the database to new volumes, using either
SQL Server log shipping or database mirroring, and then taking a brief outage as the database on the source
volumes is swapped out for the database copy on the new volumes.
Live Migration is a feature that allows the migration of volumes between SC Series arrays with zero
downtime. This allows planned migration, maintenance, and upgrades to occur without interrupting access to
SQL Server databases. In addition to avoiding the outage that would be necessary with SQL Server tools,
features such as Quality of Service (QOS) and deduplication can be used for greater control and efficiency.
QoS allows bandwidth limits and time windows to be set for data transfer. Replication deduplication can make
the data transfer more efficient by reducing the amount of redundant data that needs to be transferred,
resulting in a smaller payload.
To prepare for a Live Migration, the SQL Server host is configured to have storage mapped to both arrays
involved in the migration. Once the Live Migration is started, the data is synchronized in the background and
using Live Volume technology, I/O requests are sent to the proper array. During Live Migration, I/O is
uninterrupted and disk signatures are maintained so that SQL Server applications are unaware that any
storage changes are taking place. Performance degradation to some extent is to be expected and will depend
on connectivity and data transfer volume. Once the Live Migration is complete, volume ownership and I/O
requests are transferred to the new array. Live Migration is a great tool to use when performing planned
storage maintenance or upgrades at the same site or different sites when storage connectivity needs to be
maintained to avoid an outage. For more information consult the Dell EMC SC Series Live Migrate and
Volume Advisor best practices guide.
1.4 Online Thin Import
Thin Import is a feature that works similar to Live Migration and for the same use cases, but instead of
migrating volumes between SC Series arrays, Thin Import allows the migration of volumes from Dell EMC PS
to SC Series with minimal downtime. During the online Thin Import process, a short outage is taken to
configure Thin Import on the PS Series volume and re-present it to the host as an SC Series volume. Once
this configuration is complete, the volume can be brought back online. The data import and final cutover will
complete in the background while the applications are online. Similar to alternative SQL Server methods such
as log shipping and database mirroring a brief outage is required. Thin Import also supports QoS, allowing
bandwidth and schedule settings for data transfer. For more information on Online Thin Import consult the
Data Migration from Dell PS Series or PowerVault MD3 to Dell EMC SC Series Storage using Thin Import
deployment and configuration guide.
1.5 Replication
Creating a high availability solution for SQL Server often involves creating a copy of the data on another
storage device and synchronizing that data in some manner. Dell EMC SC Series replication provides data
synchronization between multiple arrays. Data is replicated at the volume level allowing a choice of replication
settings on a per volume basis. Using SC Series replication can be an effective way to protect SQL Server
databases due to the flexibility and configuration options that it provides. The variety of options provide a
robust way to develop a replication scheme that provides the proper mix of performance and bandwidth
efficiency while still meeting RTO and RPO requirements.