# I have a question about HAST's master slave setup.



## olav (Jul 19, 2010)

I'm reading the HAST wiki, and I have a question about it.

Lets say I have two servers, hast[a] and hast*. hast[a] is the master server. But suddenly hast[a] dies.

What happens now?
Do hast become the master server? If so, when hast[a] goes online, is hast still the master server?

Or does it work in another way?*


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## phoenix (Jul 19, 2010)

There's only 1 master and 1 slave in a HAST setup.  It never changes.

When the master goes offline, the slave takes over (what happens and how depends on the scripts you have configured).  When the master comes back online, it notifies the slave, syncs the data from the slave, and takes over.

If you have two servers marked as master, you end up with a split-brain situation that is (fairly) hard to fix (not impossible).

How it works really depends on the scripts you put in place to manage the switch (ucarp, carp+devd, etc).


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## SirDice (Jul 19, 2010)

Note: I quickly skimmed through it.

As I read it the active node is the master. So if hast[a] is the active one and hast* the backup when hast[a] fails hast will become the active node. Since the active node is the primary or master, hast will become primary/master. When hast[a] comes back online it will assume the role of secondary/backup. Perhaps one of the scripts will switch the primary role back to hast[a], I didn't look close enough.




			HAST is not responsible for selecting node's role (primary or secondary). Node's role has to be configured by an administrator of other software like heartbeat or ucarp using hastctl(8) utility.
		
Click to expand...

*


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## vivek (Jul 20, 2010)

HAST looks a lot like DRBD for FreeBSD. I'm gonna play with this weekend


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## bojan (Jul 20, 2010)

Good, so you can write a tutorial  and do some benchmark carp+hast vs heartbeat+drbd

I enjoy your blog site.


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