Hi,

We currently have 28000+ clients with 3 SEPM's (load balancing in place). I have setup another server to be a replication partner as a failover should the primary DB go offline.

What are the differences of using SEPM replication vs SQL DB mirroring? Which one should I choose and why?

The DB size is between 40-60GB.

See this thread

https://www-secure.symantec.com/connect/forums/sepm-upgrade-mirror-sql-database

Does the SEPM support use of Microsoft SQL database mirroring?

SEPM support for SQL database mirroring

The primary difference between the two, is what they protect against.

SQL Mirroring will protect against the loss of a SQL Server, whereas SEPM Replication will protect against the loss of a SEPM (and it's DB).

Which one you choose typically depends on your infrastructure and your recovery requirements.  You'll need to know about both to know which one to choose.

Assuming you already know about SQL, please see the below articles on SEPM Replication:

When to use replication with Endpoint Protection Managers

How replication works

About installing and configuring Symantec Endpoint Protection Manager for replication

Just so you know, it's entirely possible to combine the two as well, so that each replicating SEPM is supported by SQL Servers (on different boxes) which are mirrored.

What are your requirements?

Failover for Primary SQL DB only not SEPM's. When the Primary SQL server is either corrupt or offline , I would like the secondary DB to take over until the primary is restored so that clients can still receive updates and policy changes.. What would be the best option(s)?

What version of SQL are you running?

If you're looking for DB failover only, then using a SQL technology is probably best.

That said, doing so depends on your (or your company's) level of MS SQL experience.  If you have none, then setting up SEPM replication would likely be easier (as it's all wizard based, and you have SEP experience already).

If you do plan to go down the SQL route, then mirroring is relatively simple to set up, but does require some reconfiguration of the SEPM (or the use of availability groups) in the event the priamry SQL server falls over.

High level info from MS below:

http://technet.microsoft.com/en-us/library/ms190941.aspx

SQL 2012

Is there any steps to make the SEPM report to the new DB when the primary falls over then so that logs from clients would be processed to the DB.

Yup, if just using mirroring (and not availability groups, and whatnot), then in the event the primary Db falls over, you need to run the SEPM Management Server Config Wizard to point it at the secondary DB.

This is mentioned in James007's second article link (but no real details are provided).