[KLUG Members] Server Mirroring

[Jeremy Leonard]

> > I'm looking for a solution opensource or comercial to mirror data on two
> > servers in real time.
> > Something like Vinca standby server.
> > My final goal is to have a fault tolerant solution with a database.
> > Have the database mirrored to two server.
> > Use HeartBeat to fail over the actual database server application if one
> > fails.
> > I plan on having several services running on BOTH systems.
> > If all the data is mirrored to both systems then the services can be run on
> > either system.
> > Anyone know if any such mirroring software?
> 
> If by "database" you mean an RDBMS (SQL database engine): No.  ***Reliably***
> and ***consistently*** replicating an RDBMS is really really really really
> really H-A-R-D.  If you absolutely need this as a hot-pair.... buy DB2.
> 
> Otherwise you can hook two systems to a RAID cabinet and have one take over if
> the other dies; but you don't get both at the same time and they need to be
> within feet of each other (unless you can afford fiber, which is more than
> DB2).
> 
> MySQL and PostgreSQL both have hideous hacks to add brute force replication with
> very shaky atomicity,  It'll work for an application like a web forum, or maybe
> a job tracking system, but I wouldn't put it within a thousand feet of a
> business system (unless you think loosing a bunch of writes to the Accounts
> Receivable module is OK,  those guys in suits might disagree - strongly).
> 
> Honestly,  unless you have ALOT of data and thousands of users, you are better
> of with something like an x440 with internal redundancy.   I have IBM servers
> with RAID, dual power supplies, temperature monitoring, ECC RAM, etc.... they
> just don't go down.  Put it in a cabinet with its own ventilation (like the
> vent on your dryer) two UPSs and two cooling units, and your about as safe as
> your going to get. [Assuming your building has a sprinker system,  the cabinets
> are pretty sealled when closed].   Use 1U nodes like the x300's for processing,
>  you can add redundancy cheap and easy at that level;  but replicating the
> database itself is just really freakin' hard.  And a bunch of redundant servers
> all sitting in the same room.... are all going to bake or drown at the same
> time.
> 
> If you're talking about files, then perhaps GFS?


The software I want to mirror is Novell GroupWise.
I think I've found a solution. DRBD.
This will create a virtual block device that will mirror the data between two servers.
This is below the file level.
This coupled with HeartBeat should do the trick.