White Papers
BP1014 Enhancing SQL Server Protection using Dell EqualLogic Snapshot Smart Copies
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Figure 12 – Results of recovery time comparison
Conclusions from the results presented in Figure 12:
The ASM Smart copy based recovery process was approximately 7.5 times faster than the
recovery process using the native SQL Server® backup utility for recovering the database to
the same point (which involves restore plus log replay).
Instead of a typical restore process that involves first restoring a full backup (and then any
differential or incremental log backups) in a recovery scenario, restoring to a point in time
using EqualLogic smart copy snapshot is much more efficient.
We did not use SQL Server® differential backups in this test. Differential backups are
commonly used, and they can help to accelerate recovery times just as we are showing with
use of Smart Copies. Even if SQL differential backups were created at the same times that ASM
Smart Copies were, the Smart Copy based method would still have been at least 3 times faster,
based on comparison to just the full backup restore and log backup recovery time
components.
To explain why the EqualLogic based ASM Smart Copy method provides much faster recovery times it
is important to understand the difference in data flow that occurred during each of the recovery
processes we tested. For Test 1, the copy-restore processes for the full backup and for the transaction
log backups both read from files stored in the backup data volumes in the backup pool. In Test 2, the
in-place restore of the Smart Copy snapshot does not cause data to be copied across the SAN from
the backup pool to the SQL Server® data pool. Instead, the Smart Copy in-place restore just restores
the data volume hosting the database to the most recent volume snapshot. No read/write I/O
operations are required to do this. This is why an in-place restore from a Smart copy will typically take
much less time to complete than a full database restore when using the SQL Server® native backup
utility. This is illustrated in the difference between data flow patterns between Test 1 and Test 2, as
shown in Figure 13 and Figure 14 below.