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Terms and technologies

This section defines the terms and technologies referenced in this guide. Each term or technology is described within a SnapManager-specific context.

Availability Group
A part of the Microsoft SQL Server 2012 AlwaysOn feature. It combines both database mirroring and log shipping capabilities to enable:
  • Multi-database failover
  • Multiple secondaries
  • Application failover using virtual names
  • Readable secondary
  • Backup from secondary
The databases as a group can move from one node to another node (failover) within the AlwaysOn set of nodes.
AlwaysOn
A disaster recovery solution added in Microsoft SQL Server 2012. The solution provides both database level and instance level availability.
backup set
A backup set consists of metadata located in the SnapInfo directory structure and Snapshot copies. The Snapshot copies are created in volumes containing LUNs, SMB shares, and VMDKs used by databases that are contained in the backup set.
cluster group
A logical group of cluster resources that can be moved from one node to the other while the nodes remain operational. The cluster group can be moved by the administrator, or it can be moved as a result of a cluster resource failure.
database
A database is a collection of logical objects within a physical structure. The physical structure consists of one or more data files, and one or more transaction log files. A database is either used by the SQL Server itself (system database) or by an application (user database).
Database Consistency Checker (DBCC)
The Microsoft SQL Server utility for finding and correcting problems in the consistency of the database.
host system
A computer that accesses storage on a storage system.
log shipping
A process that takes backed-up transaction logs from a primary SQL Server and applies them sequentially on a scheduled basis to another SQL Server database. If a failure occurs, an application could be redirected to the other server, which would be only slightly behind the primary database. Log shipping is a means of protecting organizations if a logical or physical system failure occurs.
MSCS
Microsoft Cluster Services (MSCS) are system services that make it possible to create a virtual system consisting of multiple cluster nodes; each node is an independent physical computer and is a failover resource of other nodes in the cluster. Each node can support one or more virtual SQL Server instances.
multiple-instance cluster
A multinode cluster with multiple virtual SQL Server instances. Each node can be active, running one or more virtual SQL Server instances or passive. The passive node is an idle system waiting for another node to fail over and thereby becoming an active node. If one system fails, the other system takes over its application services.
quorum disk
A shared disk resource that is used by MSCS to keep track of cluster management information, such as cluster resources and state. The quorum disk should not be used for SQL Server files. The quorum disk is a single-point-of-failure.
recovery model
There are three distinct ways that you can recover your SQL Server databases if a failure occurs. Each model addresses a different need for performance, disk and tape space, and protection against data loss. The three models are summarized as follows:
Simple
It only supports database backup and not transaction log backup. Since there is no log backup, you cannot perform an up-to-the-minute restore. SnapManager for SQL Server only supports point-in-time restore operations for databases in Simple recovery mode.
Full
All transactions are logged.
Bulk logged
Certain database operations (including SELECT INTO, BULK COPY/BCP, CREATE INDEX, WRITETEXT, and UPDATETEXT) are logged minimally. Database pages changed by committed bulk-logged operation are copied to the backed-up transaction log. The Bulk logged model has a higher risk of data loss than the Full recovery model.

For more information, see your Microsoft SQL Server documentation.

single-instance cluster
(active/passive mode) refers to an MSCS cluster with SQL Server installed, where only one active instance of SQL Server is owned by a node and all other nodes of the cluster are in a standby state.
SQL
Structured Query Language.
SQL Server
A Microsoft relational database system based on the client-server database model.
SQL Server computer
The hardware on which a Microsoft SQL Server database system is running.
SQL Server replication
A process that is initiated and controlled by the database engine (SQL Server).
system database
A type of database that is used internally by SQL Server. System databases are created either during installation or during feature configuration, such as the distribution database.
distribution database
A database on the distributor that stores data for replication, including transactions, Snapshot jobs, synchronization status, and replication history information. The database is created when replication is activated.
master database
Records the system-level information, SQL Server initialization information, and configuration settings for SQL Server. This database also records all login accounts and the mapping information from the name of a database to its primary file location.
tempdb database
A database that is used to fulfill all temporary storage needs, including stored procedures and tables. The tempdb database uses SQL Server during query processing and sorting, and for maintaining row versions used in Snapshot isolation. A clean copy of the tempdb database is re-created with its default size every time SQL Server is started.
model database
A template for all other databases on the system, including the tempdb database. When a database is created, the first part of it is created as a copy of the contents of the model database. The rest of the database is filled with empty pages. The model database must exist on the system because it is used to re-create tempdb every time SQL Server is started. You can alter the model database to include user-defined data types, tables, and so on. If you alter the model database, every database you create has the modified attributes.
msdb database
A database that holds tables that SQL Server Agent uses for scheduling jobs and alerts and for recording operators (those assigned responsibility for jobs and alerts). This database also holds tables used for log shipping and for backup and recovery.
transaction log
A file that is used as a write-ahead log. All transactional operations are recorded in the transaction log; a transaction is considered committed when the 'commit' transaction record has been written to the transaction log. The main purpose of the transaction log is for crash consistency; if there is a system crash, power failure, or similar disastrous event, then the transaction log has enough information to roll forward all committed transactions and roll back all noncommittal transactions.
user database
A database created for and used by an application is considered to be a user database.
Windows Server Failover Cluster (WSFC)
The set of servers (nodes) on which AlwaysOn is configured. The nodes do not share disks and each node must have an SQL Server instance.