Storage Systems - SQL Server 2012 Internals and Troubleshooting - page 90

snap volume. Fracturing is the process of stopping the cloning operation and making the snapshot
or clone volume ready for use. Once the fracture is complete, the database resumes normal write
operations. Reads are not affected.

WARNING VDI imposes a ten-second timer for the completion of the freeze and
fracture operation. When implementing VDI on busy SQL Servers, especially
those with large memory, it may be necessary to stop running SQL Server jobs
prior to executing the freeze and fracture operation. If the SQL Server can't write
all the dirty data pages to disk in ten seconds, the operation will fail.

Crash-consistent data copies depend on the fact that SQL Server uses a write-ahead logging model,
as described earlier. New data is i rst written to the disk or storage volume. As soon as the write
operation is complete, it is acknowledged. Only after the data has been successfully written and
acknowledged will SQL Server write data to its buffer pool.

WARNING SQL server offers features to improve data loading. These features
change how data is written and can affect SQL Server replication. Microsoft
offers detailed information on data loading with Trace Flag 610: http://msdn
.microsoft.com/en-us/library/dd425070(v=SQL.100).aspx .

If the database is shut down before it has a chance to
l ush dirty buffer-page data to disk, the write-ahead
logging feature enables SQL Server to recover data that
was written to the log but not to the database i les. This
recovery model enables the use of advanced replication
technologies.

Storage Array

Clone data volumes create an exact replica of the source
volume as of the point in time when the clone was cre-
ated (Figure 4-9). Because the clone is an exact copy it
enables the isolation of I/O performance. The source
volume can continue to operate normally while the
clone can be mounted to a different host. This enables
a workload to be distributed among many machines
without affecting the source volume. Such a scenario is
extremely useful to enable high-performance reporting
systems. Keep in mind that the clone volume requires
the same amount of space within the storage array
as the original volume requires.

Replication

Source
Disk

Clone 1

Clone 2
Fractured
10 pm

FIGURE 4-9