Stellar failure safety is defined as n = 3f+1 <=> f = (n-1)/3 n is number of node and f is failure safety.

I have setup 3 nodes with my quorum and THRESHOLD_PERCENT=67 but it is not allowing my quorum.


    2018-04-18T13:24:05.024 <startup> [default ERROR] Can't have FAILURE_SAFETY=0 unless you also set UNSAFE_QUORUM=true. Be sure you know what you are doing! [Config.cpp:596]
    2018-04-18T13:24:05.024 <startup> [default INFO]  Current QUORUM_SET breaks with 1 failures
    2018-04-18T13:24:05.024 <startup> [default FATAL] Got an exception: SCP unsafe [main.cpp:917]

din't get exactly what is wrong, any explanation? FAILURE_SAFETY is set to default -1.

1 Answer 1


It says Can't have FAILURE_SAFETY=0 unless you also set UNSAFE_QUORUM=true. I guess you might have set somewhere FAILURE_SAFETY=0.

In the example config, it says

A value of 0 is only allowed if UNSAFE_QUORUM is set

Therefore, your log showed Got an exception: SCP unsafe. To fix this, you have to declare UNSAFE_QUORUM=true.

As you have 3 nodes, n=3 <=> f<1.

Less than 1 node can malfunction while the consensus network still works, i.e. Your network can tolerate ZERO node to malfunction.

It makes sense for you to put FAILURE_SAFETY=0, but you also have to set UNSAFE_QUORUM=true.

  • default FAILURE_SAFETY is -1, so in my case this calculate f<1, if i don't put FAILURE_SAFETY in my config this auto assume FAILURE_SAFETY to zero ?
    – Sohan
    Commented Apr 19, 2018 at 5:55
  • No, the default value is -1. If you don't modify it explicitly, FAILURE_SAFETY takes the default -1. The value always assumes it is -1; it won't change to zero automatically.
    – cesarm
    Commented Apr 19, 2018 at 8:49

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