Posted by aleu@vp.pl on 09/30/07 02:46

Roy Harvey (SQL Server MVP) wrote:
> The best place to ask this is microsoft.public.sqlserver.replication.
>
> I am no replication expert, but your requirement sounds like it needs
> Database Mirroring. I am guessing that a T1 would be a bit slow for
> synchronous mode, also known as high-safety mode. "Under high-safety
> mode, when a session begins, the mirror server synchronizes the mirror
> database with the principal database as quickly as possible. Once the
> databases are synchronized a committed transaction is committed on
> both partners, at the cost of increased transaction latency."
>
> That would leave asynchronous operation mode, also known as
> high-performance mode. "The mirror server attempts to keep up with
> the log records sent by the principal server. The mirror database
> might lag somewhat behind the principal database, though, typically,
> the gap between the databases is small. However, the gap can become
> substantial if the principal server is under a heavy work load or the
> system of the mirror server is over loaded."
>
> "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, without waiting 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
> permits the principal server to run with minimum transaction latency,
> at the risk of some potential data loss."
>
> The quotes are straight from BOL.

Roy,

Thanks for the provided information. Is there any information on how
much bandwidth is required to perform the synchronous mode successfully
(I was considering purchasing second T1 link for redundancy anyway)?
Would this be sufficient? What happens in both synchronous and
asynchronous cases, when you loose the connectivity between the two
databases lets say for 10 minutes?

Could you please provide me with some links on MSSQL 2005 mirroring
options/requirements/best practices?

Thanks,
AL

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