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.

On Sat, 29 Sep 2007 22:46:44 -0400, "aleu@vp.pl" <aleu@vp.pl> wrote:

>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

Roy Harvey (SQL Server MVP) wrote:
> If you loose connectivity for ten minutes it would have two impacts.
> One, once the connection is re-established there is an additional
> delay while the backlog is cleared. Two, you could not clear the
> transactions from the log on the source system until after the
> connection is re-established and the backlog cleared.
>
> I don't have the hands-on experience with mirroring to have a good
> feel for bandwidth requirements, but the major variable is the level
> and nature of database activity that only you know. Reading a bit
> more from some googled items I am more and more thinking you would be
> restricted to asynchronous. If you take a look at your transaction
> logs they should give you some idea how much data has to be pushed
> over the link.
>
> I suggest googling sql server 2005 mirroring and reading up. And
> hoping someone with hands-on experience joins the discussion!
>