What are the best practices for SQL Server capacity planning and hardware sizing?

Capacity planning and hardware sizing are important considerations for SQL Server performance and scalability. It is essential to ensure that the hardware and resources allocated are sufficient to support the workload of the database. Below are some best practices for SQL Server capacity planning and hardware sizing:

1. Understand the workload: Before making any capacity planning or hardware sizing decisions, it is important to understand the workload of the database. This includes the size of the database, the number of users, the type of application, and the types of queries that are executed.

2. Plan for growth: It is important to plan for future growth when sizing hardware and capacity. This includes considering the expected growth rate of the database, as well as any future application or user requirements.

3. Choose the right hardware: The hardware chosen for SQL Server should be able to handle the workload of the database. This includes the number of CPUs, amount of RAM, and storage capacity. It is important to choose hardware that is scalable, so that it can be upgraded as the workload increases.

4. RAID configuration: RAID (Redundant Array of Independent Disks) can improve performance and provide redundancy in the event of disk failure. It is important to choose the right RAID configuration based on the workload of the database.

5. Use SSDs for storage: Solid State Drives (SSDs) can significantly improve SQL Server performance, compared to traditional hard drives. SSDs are faster at random access, which is important for databases that have a lot of random reads and writes.

6. Virtualization: Virtualization can be used to optimize hardware utilization, which can reduce costs. However, it is important to ensure that the virtual environment can support the workload of the database.

7. Monitor performance: Regularly monitoring SQL Server performance can help identify any hardware or capacity issues. This includes measuring CPU utilization, memory usage, and disk I/O performance.

Here is an example SQL script to get basic performance metrics from SQL Server:

SELECT 
    GETDATE() AS [Date and Time],
    cpu.time_ticks / CONVERT(FLOAT, cpu.cntr_value) AS [CPU usage %],
    mem.cntr_value / 1024 AS [Memory usage (MB)],
    disk.cntr_value / 1024 AS [Disk I/O usage (MB/s)]
FROM 
    sys.dm_os_performance_counters cpu
    INNER JOIN sys.dm_os_performance_counters mem ON cpu.object_name = mem.object_name
    INNER JOIN sys.dm_os_performance_counters disk ON cpu.object_name = disk.object_name
WHERE 
    cpu.counter_name = 'Processor Time' AND
    cpu.instance_name = '_Total' AND
    mem.counter_name = 'Target Server Memory (KB)' AND
    mem.instance_name = '[Default]' AND
    disk.counter_name = 'Disk Read Bytes/sec' AND
    disk.instance_name = '_Total'

This SQL script will return the CPU usage percentage, memory usage in MB, and disk I/O usage in MB/s. These metrics can be used to identify any hardware or capacity issues and make necessary adjustments.