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SQL Server design considerations
8 Dell EMC PowerVault ME4 Series and Microsoft SQL Server | 3923-BP-SQL
There is a variety of other RAID levels and storage configurations available for very specific workloads. Make
sure the design tradeoffs are completely understood when choosing custom configurations and settings. In
many cases, modifying the storage configuration for existing volumes will involve halting I/O on those
volumes, resulting in a SQL Server outage. For detailed information on all available choices, including
ADAPT, consult the ME4 Series Administrator’s Guide.
3.4.2 RAID levels and performance
The performance characteristics of the ME4 Series are largely dependent on the RAID level chosen for the
storage configuration. While the ADAPT RAID level provides the most balanced configuration, other RAID
levels are available for maximum performance or maximum capacity. The two additional levels discussed in
this section are RAID 5 and RAID 10. For all available RAID levels, consult the ME4 Series Administrator’s
Guide. The performance numbers presented are maximum values on an ME4 Series array with a minimum of
24 drives and two storage pools, one per controller.
Note that performance among RAID levels only has significant variation in workloads such as OLTP where
frequent writes occur. For read-only workloads such as OLAP, there is practically no performance benefit to
select RAID levels based on performance.
Use care when configuring multiple RAID levels on the same ME4 Series array. Ensure that the number of
drives in the storage pool is sufficient to provide the performance desired. Mixing RAID levels within a storage
pool is not recommended.
Remember that when selecting RAID levels, there are design considerations other than performance. RAID
levels impact the data protection, capacity, and flexibility of the overall storage design. Therefore, finding the
best balance of performance, data protection, capacity, and flexibility is the goal.
3.4.2.1 ADAPT
When using the ADAPT RAID level, the ME4 Series can perform up to 99,000 IOPS using an OLTP
workload
1
and up to 7 GB/sec for OLAP workloads
2
. The solid OLTP performance and outstanding read
performance, as well as the balance of performance, capacity, and data protection, make ADAPT a good
choice for mixed-database workloads.
3.4.2.2 RAID 5
When additional performance and capacity is required, RAID 5 may be used. In a RAID 5 configuration, some
disk resources that were reserved for data protection are utilized for additional capacity and performance.
Therefore, RAID 5 offers less data protection than ADAPT. However, it can deliver up to 115,000 IOPS for
OLTP workloads
1
.
3.4.2.3 RAID 10
For maximum OLTP performance, RAID 10 can deliver up to 192,000 IOPS for OLTP workloads
1
. In a RAID
10 configuration, the usable capacity is reduced to 50% of raw capacity. Therefore, a RAID 10 solution
requires almost double the number of drives compared to more space-efficient RAID types.
1
An OLTP workload is defined as having an 8k block size and a 70/30 read/write mix.
2
An OLAP workload is defined as having a 128k+ block size with 100% reads.