[dba-SQLServer] sql server 2005 database mirroring - howmany copies of sql server?

Hi Jim:

Not sure if it is publishing or subscribing in this scenario. Are you 
talking about (snapshot) replication?

Database mirroring is new in sql server 2005, which is a bit different than 
replication.  in database mirroring, there is a principal database, which is 
what client accesses. if the principal database is disconnected, the witness 
tells the mirror server to become the principal server; the failover is 
automatic and transparent to the client; replication is like database 
mirroring because there are two copies of the db except that in db 
mirroring, the client only sees one database. replication probably good for 
WANs; for db mirroring, it is preferred that all servers are on same domain 
over standard network infrastructre.

Billy


>From: Jim Lawrence <accessd at shaw.ca>
>Reply-To: dba-sqlserver at databaseadvisors.com
>To: dba-sqlserver at databaseadvisors.com
>Subject: Re: [dba-SQLServer] sql server 2005 database mirroring - 
>howmany	copies of sql server?
>Date: Wed, 14 Sep 2005 22:19:35 -0700
>
>Hi Billy:
>
>Do you mean Publishing and Subscribing? I have setup two versions of SQL
>server (2000 Enterprise and 2000 Development) on a couple of computers and
>have tested them passing data back and forth... It is quick process,
>something like Access synchronizing but at this time it is no more than a
>local backup.
>
>Jim
>
>-----Original Message-----
>From: dba-sqlserver-bounces at databaseadvisors.com
>[mailto:dba-sqlserver-bounces at databaseadvisors.com] On Behalf Of Billy Pang
>Sent: Wednesday, September 14, 2005 7:58 PM
>To: dba-SQLServer at databaseadvisors.com
>Subject: [dba-SQLServer] sql server 2005 database mirroring - how many
>copies of sql server?
>
>Hello:
>
>I need someone to clarify database mirroring for me.  How many copies of 
>sql
>
>server do I need to configure a database mirroring session involving three
>separate servers (that includes a witness server)?
>
>The scenario is this: in the quorum, there are three servers: the principal
>server, the mirror server and the witness server.  the principal server has
>the original db; the mirror server has a copy of the db on principal 
>server;
>
>the witness server watches both the principal server and the mirror server.
>
>If the principal server goes down, the witness automatically tells the
>mirror server to take over as principal server, a process that takes 3
>seconds.
>
>To establish the mirror session for all three servers, according MS
>eLearning course 2938, I perform the following:
>
>For the principal server's participation in the quorum:
>1) from the principal server, I run the alter database statement on the
>original db
>
>For the mirror server's participation in the quorum:
>2) from the mirror server, I run the alter database statement on the mirror
>db
>
>For the witness server's participation in the quorum:
>3) from the PRINCIPAL server, I run the alter database statement on the
>original db
>
>Given step 3), I can't tell if I need 2 or 3 copies of sql server (ie. do I
>need a copy of sql server on the witness server?)  Am I missing something
>here?
>
>Thanks in advance,
>Billy
>
>
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