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VMware SQL Server Plug-in Automatic Filter Discovery (1009519)
Purpose
This article provides information about how VMware SQL Server Plug-in for Microsoft SQL Server discovers new information during normal operation.
Resolution
Database structure in Microsoft SQL Server can be divided into two areas:
Logical structure – the arrangement of the data into tables, the relationships between data in different tables, and the queries, views and other structures that allow the data to be manipulated, profiled and presented to the end-user.
Physical structure – the physical arrangement of data files and transaction logs on the host server(s).
VMware SQL Server Plug-in protects the physical structure of a SQL Server database. In so doing, it automatically protects the logical structure as well.
Physical Database Structure
SQL Server uses two types of files to store data:
Data files (.MDF, .NDF), which act as a repository for all SQL Server data
Transaction logs (.LDF), which are used to ensure data integrity is maintained at the level of individual transactions
VMware SQL Server Plug-in protects and replicates data files and transaction logs from the active server to the passive server.
SQL Server Instances
An Instance of SQL server is a complete, independent installation of the entire SQL Server database engine. SQL Server instances are essentially independent of one another. A physical server may support up to 16 SQL Server instances. One of these instances is termed the Default instance; the other 15 are Named instances.
For each SQL Server instance, VMware SQL Server Plug-in detects and monitors two services:
For the Default instance:
MSSQLSERVER
SQLServerAgent
For any Named instances:
MSSQL$
SQLAgent$
In addition, the Microsoft Search Service (MSSEARCH) is also detected and monitored. If any of these services stops unexpectedly, VMware SQL Server Plug-in detects this and performs one or more user-defined recovery operations on that service.
Each SQL Server Instance can support up to 32,767 databases. Each individual database can in turn contain up to 32,767 data files divided across a maximum of 256 file groups. In practice, the number of databases, and the number of files and file groups per database, is usually far smaller.
Default Data File Locations
Every Instance of SQL Server has a default directory where all the data files and transaction logs for that instance are stored, unless the user chooses a different directory. The location of this default directory is stored in the Windows registry.
VMware SQL Server Plug-in protects this location with a filter terminating in a recursive wildcard (\**), meaning that all files and folders under the protected directory are replicated from the active to the passive server. If SQL Server is installed in its default location, the filter looks like:
VMware SQL Server Plug-in obtains these locations by querying the Windows registry.
User-Specified Data File Locations
In addition, SQL Server data files and transaction logs may be placed in any user-specified location. This may be done for performance reasons - it may, for example, be desirable to place data files and transaction logs on different physical disks.
VMware SQL Server Plug-in protects such files on a per-file basis, using specific filters which name only the protected file. The filters may appear as:
C:\SQLServerData\MyDatabase\MyDataFile.MDF
D:\MoreData\MyOtherDataFile.LDF
E:\SQL Server\Transaction Logs\MyLog.LDF
VMware SQL Server Plug-in determines these locations by querying the master database for each SQL Server instance.
Other protected locations
VMware SQL Server Plug-in creates filters for some other default SQL Server directories, which are not directly related to data file or transaction log storage.
Additional Information
vCSHB-Ref-398
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