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Mirroring Questions


Mirroring Questions Ian Jenkins, MCSD
5/24/2006 10:54:04 AM
sql server replication:
Looking for some answers about Microsoft SQL Server 2005's new
mirroring technology.

1) When using a witness what happens if the witness crashes?

2) What happens if the Principal crashes and the mirror never becomes
the Principal?

3) What happens if you try to insert records into the mirror directly?

4) When using SQL Native Client is a witness necessary? Don't you
supply the mirrored server in the database connection?

Thanks,
Ian Jenkins, MCSD
Re: Mirroring Questions Hilary Cotter
5/28/2006 12:00:00 AM
1) Witnesses are used for High Availability mode. If the witness crashes,
the principal will still think its the principal and the client will keep on
using it. From

http://www.microsoft.com/technet/prodtechnol/sql/2005/dbmirror.mspx
The witness is not considered a single point of failure in a database
mirroring session, because if the witness server fails, the principal and
mirror continue to form a quorum. (For further information, see the topic
"Quorum in Database Mirroring Sessions" in SQL Server Books Online.)

2) If the principal fails in High Availability mode the client will be
reconnected to the mirror. If for some reason the mirror does not become the
new principal it will be inaccessible.

3) You can't, its read only. You can create point in time database snapshots
on it however.

4) No, its not necessary, but in high availability mode both are necessary.
--
Hilary Cotter
Director of Text Mining and Database Strategy
RelevantNOISE.Com - Dedicated to mining blogs for business intelligence.

This posting is my own and doesn't necessarily represent RelevantNoise's
positions, strategies or opinions.

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