SQL 2005 Mirroring questions

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Kirsten - 16 Sep 2005 20:14 GMT

I'm testing SQL 2005's Mirroring capabilities.
I need to implement a high-availability solution to the 1-server problem,
but without a cluster server ($$$$).
So SQL Mirroring is the key.

SERVER_A (main) and SERVER_B (backup) holds replicated data. SERVER_C is the
"Synchonize server" (I think it is called Witness).

My question is about SERVER_C:
1) does it need to be on a separate server or it can be a second instance in
SERVER_A (or B)?

2) What happens if C fails?

3) Clients connect C or to main server A?

4) Is it possible to have a SERVER_D witness if C fails?

5) When I'm taking down SERVER_A for maintainance (for ex): is there any
command to stop current actity (like drainstop in Network Load Balancing)?

Thanks!

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Brian Lawton - 16 Sep 2005 20:26 GMT

Since SQL 2005 is still in beta, you'll want to post this in the Community
Newsgroups:

http://communities.microsoft.com/newsgroups/default.asp?icp=sqlserver2005&slcid=us

But you should also consider this update from yesterday noting that the
mirroring functionality will be delayed until 2006.

http://www.microsoft.com/sql/2005/productinfo/letter.mspx

Signature

--Brian
(Please reply to the newsgroups only.)

> I'm testing SQL 2005's Mirroring capabilities.
> I need to implement a high-availability solution to the 1-server problem,
[quoted text clipped - 20 lines]
>
> Thanks!

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Joe Yong - 21 Sep 2005 14:29 GMT

DB Mirroring is a great feature but it'll take more than 1 post to figure
out. Suggest you check out www.microsoft.com/sql/2005 to get more info on DB
Mirroring to ensure you're really protecting your system appropriately and
have the right barriers to availability addressed. In the meantime, see
below for some short notes on your questions.

joe.

> I'm testing SQL 2005's Mirroring capabilities.
> I need to implement a high-availability solution to the 1-server problem,
> but without a cluster server ($$$$).
> So SQL Mirroring is the key.

[jy] Totally understand the $$$ bit but DB Mirroring isn't free either. At
the end of the day, you need to figure out what's it gonna cost you if your
system goes down for extended periods. Kinda like insurance or even AAA. How
often do you wreck your car or how often does your car breakdown? Why do
most people still have comprehensive insurance coverage and why are there so
many auto-club members? :-)

> SERVER_A (main) and SERVER_B (backup) holds replicated data. SERVER_C is
> the
> "Synchonize server" (I think it is called Witness).

[jy] Not a synchronize server. The witness just keeps track of who's
"really" alive and allows automated failover without getting a split brain.

> My question is about SERVER_C:
> 1) does it need to be on a separate server or it can be a second instance
> in
> SERVER_A (or B)?

[jy] Technically it's just another SQL Server instance but it kinda defeats
the purpose since you risk losing the witness along with one of the
instances when a node goes down. Not recommended.

> 2) What happens if C fails?

[jy] You lose the ability to have automatic failover.

> 3) Clients connect C or to main server A?

[jy] You connect to either A or B. The witness does not hold user data.
Please review the documentation in SQL Server 2005 Book Online on Database
Mirroring.

> 4) Is it possible to have a SERVER_D witness if C fails?

[jy] You can cluster C. :-)

> 5) When I'm taking down SERVER_A for maintainance (for ex): is there any
> command to stop current actity (like drainstop in Network Load Balancing)?

[jy] Not "really". There are a few ways to prevent new connections but at
the end of the day the mirror server (B) does not take over until explicitly
told to.

> Thanks!

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