Microsoft sql server mirroring

Could you be a little more specific please? A witness can be any edition of SQL Server. If you have a few instances around that are in the same datacenter as the principal, I would choose one that should generally be available.

If multiple datacenters are used, you could choose it to be at a seperate one from either the principal or the mirror as long as the connection is generally available between all of them. It can either be an instance you currently have running in your environment or you could install something like express edition on a server to use just as a witness. This is really a design choice that should be made given your current infrastructure.

I would not put it on the same server as your principal even if there are multiple instances as a loss of the principal would also mean a loss of the witness. You're correct, it's completely different from WSFC. Mirroring protects at a database level through the transaction log, WSFC protects at the instance level by having redundant hardware. You could, but I would be wary of putting other services on it before testing.

If you're going to do WSFC, I wouldn't have the mirror and the principal on the same cluster - just to keep things highly available. The point of mirroring is to have a redundant copy of the database up-to-date and ready for action shuold the need arise. Since mirroring happens at a database level, you'll have to have a plan if only a single database fails to the mirror.

I currently have Lync in my environment and it used multiple databases that rely on each other being in the same instance - and it relies on cross database overship chaining which means all of the databases need to be on the same instance. You'll want to see if this is something that you'll want to deal with in your environment.

There are a few scripts available that can fail all databases over to the mirror if one database fails. You've stated that the instance will be , I would like to point out that database mirroring is a deprecated feature in , replaced by always on. You may want to look into availability groups instead of mirroring. My question is Lync requires SQL server mirroring as well as File share for other stuff, i thought i would install WSFC and make file share highly availble where quortum disk and another disk will be part of WSFC, on the same servers i would install sql server and will mirror the required database but sql servers will not part of WSFC at all, is it supported by microsoft or not, can i do it.

So you mean to say that i should choose a seperate server with windows and install sql express edition on it to make a witness server have i understood correct, if yes that means it is like WSFC file share witness which could be on another server which is not part of the WSFC. For Question Number 1, yes i want the over all best practise in terms of deployment, planning and considerations of sql server mirroring.

Office Office Exchange Server. Not an IT pro? The database mirroring synchronous mode guarantees that the log chain is unaffected by a mirroring failover and that only valid log is restored. The secondary servers continue to copy log backups without knowing that a different server instance has become the primary server. When using a local log shipping monitor, no special considerations are necessary to accommodate this scenario.

For information about using a remote monitoring instance with this scenario, see, "The Impact of Database Mirroring on a Remote Monitoring Instance," later in this topic. The following figure shows how log shipping and database mirroring work together when mirroring is running in high-safety mode with automatic failover.

To maximize availability of the log shipping session, the backup location is on a share directory on a separate host computer. After a mirroring failover, the primary server name defined on the secondary server is unchanged.

When log shipping uses with a remote monitoring instance, combining the log shipping session and database mirroring affects the information in the monitor tables. To keep monitoring as seamless as possible, when you use a remote monitor, we recommend that you specify the original primary name when configuring the primary at the secondary.

Set up database mirroring. Set up log shipping on the principal database as the primary database for one or more secondary databases. You should set up a single share as the backup directory a backup share.

This ensures that after role switching between the principal and mirror servers, backup jobs continue to write to the same directory as before. A best practice is to ensure that this share is located on a different physical server from the servers hosting the databases involved in mirroring and log shipping. Therefore, you must use stored procedures to set up the new principal as primary. Skip to main content. This browser is no longer supported.

Typically, these server instances reside on computers in different locations. Starting database mirroring on a database, initiates a relationship, known as a database mirroring session , between these server instances. One server instance serves the database to clients the principal server. The other instance acts as a hot or warm standby server the mirror server , depending on the configuration and state of the mirroring session.

When a database mirroring session is synchronized, database mirroring provides a hot standby server that supports rapid failover without a loss of data from committed transactions. When the session is not synchronized, the mirror server is typically available as a warm standby server with possible data loss.

The principal and mirror servers communicate and cooperate as partners in a database mirroring session. The two partners perform complementary roles in the session: the principal role and the mirror role. At any given time, one partner performs the principal role, and the other partner performs the mirror role.

Each partner is described as owning its current role. The partner that owns the principal role is known as the principal server , and its copy of the database is the current principal database. The partner that owns the mirror role is known as the mirror server , and its copy of the database is the current mirror database.

When database mirroring is deployed in a production environment, the principal database is the production database. Database mirroring involves redoing every insert, update, and delete operation that occurs on the principal database onto the mirror database as quickly as possible. Redoing is accomplished by sending a stream of active transaction log records to the mirror server, which applies log records to the mirror database, in sequence, as quickly as possible.

Unlike replication, which works at the logical level, database mirroring works at the level of the physical log record. Beginning in SQL Server , the principal server compresses the stream of transaction log records before sending it to the mirror server. This log compression occurs in all mirroring sessions.

A given server instance can participate in multiple concurrent database mirroring sessions with the same or different partners.

A server instance can be a partner in some sessions and a witness in other sessions. The mirror server instance must be running the same edition of SQL Server. A database mirroring session runs with either synchronous or asynchronous operation.

Under asynchronous operation, the transactions commit without waiting for the mirror server to write the log to disk, which maximizes performance.

Under synchronous operation, a transaction is committed on both partners, but at the cost of increased transaction latency. There are two mirroring operating modes. One of them, high-safety mode supports synchronous operation. Under high-safety mode, when a session starts, the mirror server synchronizes the mirror database together with the principal database as quickly as possible. As soon as the databases are synchronized, a transaction is committed on both partners, at the cost of increased transaction latency.

The second operating mode, high-performance mode , runs asynchronously. The mirror server tries to keep up with the log records sent by the principal server. The mirror database might lag somewhat behind the principal database. However, typically, the gap between the databases is small.

However, the gap can become significant if the principal server is under a heavy work load or the system of the mirror server is overloaded. In high-performance mode, as soon as the principal server sends a log record to the mirror server, the principal server sends a confirmation to the client. It does not wait for an acknowledgement from the mirror server. This means that transactions commit without waiting for the mirror server to write the log to disk.

Such asynchronous operation enables the principal server to run with minimum transaction latency, at the potential risk of some data loss. All database mirroring sessions support only one principal server and one mirror server.

This configuration is shown in the following illustration. High-safety mode with automatic failover requires a third server instance, known as a witness. Unlike the two partners, the witness does not serve the database.

The witness supports automatic failover by verifying whether the principal server is up and functioning. The mirror server initiates automatic failover only if the mirror and the witness remain connected to each other after both have been disconnected from the principal server.

Establishing a new mirroring session or adding a witness to an existing mirroring configuration requires that all involved server instances run the same version of SQL Server. However, when you are upgrading to SQL Server or a later version, the versions of the involved instances can vary.

Whether an operating mode is asynchronous or synchronous depends on the transaction safety setting. If you exclusively use SQL Server Management Studio to configure database mirroring, transaction safety settings are configured automatically when you select the operation mode. If you use Transact-SQL to configure database mirroring, you must understand how to set transaction safety.