Cluster Shared Volumes vs Traditional Drive Letters
By Tom Nonmacher
The choice between Cluster Shared Volumes (CSV) and traditional drive letters can have a significant impact on your database performance, scalability, and manageability, particularly when it comes to SQL Server 2016 and SQL Server 2017. Both have their strengths and weaknesses, and understanding these can help you make an informed decision. This post will explore the pros and cons of each, and provide some practical examples using SQL Server 2016, SQL Server 2017, MySQL 5.7, DB2 11.1, and Azure SQL.
Traditionally, SQL Server instances were assigned individual drive letters. This approach was straightforward and easy to manage, but it was also limited by the number of available drive letters. As databases grew larger and more numerous, this became a significant constraint. Enter Cluster Shared Volumes, a feature that was introduced with SQL Server 2016. CSV allows multiple SQL Server instances to read and write to the same drive simultaneously, circumventing the drive letter limitation.
One of the key advantages of CSV is its improved scalability. With traditional drive letters, you're limited to 26 mounts (A-Z). With CSV, there's virtually no limit. This makes CSV an excellent choice for large-scale deployments, where many SQL Server instances need to access the same data.
-- Example of SQL Server 2017 using CSV
USE master;
GO
ALTER DATABASE TestDB SET SINGLE_USER WITH ROLLBACK IMMEDIATE;
GO
ALTER DATABASE TestDB SET MULTI_USER;
GO
However, CSV is not without its downsides. Because multiple instances can access the same volume, there's a greater risk of contention and performance degradation. To mitigate this, it's essential to carefully manage your workloads and monitor performance regularly. In contrast, traditional drive letters offer more predictable performance, since each SQL Server instance has its own dedicated drive.
Another consideration is compatibility. While CSV is supported by SQL Server 2016 and later, it's not compatible with earlier versions. Furthermore, CSV is not supported by all database systems. For example, MySQL 5.7 and DB2 11.1 do not support CSV, and instead rely on traditional drive letters or other forms of storage management. Azure SQL, on the other hand, uses Azure Storage, which provides its own set of benefits and trade-offs.
-- Example of MySQL 5.7 using traditional drive letters
CREATE DATABASE TestDB;
USE TestDB;
CREATE TABLE TestTable (ID INT, Name VARCHAR(20));
INSERT INTO TestTable VALUES (1, 'Test');
SELECT * FROM TestTable;
In conclusion, the choice between CSV and traditional drive letters largely depends on your specific needs and the database system you're using. CSV offers greater scalability, but it may require more careful management and monitoring. Traditional drive letters, on the other hand, offer predictable performance and compatibility with a wider range of database systems. As always, it's important to thoroughly test and evaluate both options in your specific environment before making a decision.