I found out that proxmox doc says a lot abou Fencing. I haven't found anything about it in Ganeti doc. Also I screeched Ganeti Google Group Archive and I found similar question but answer was that Split Brain is not a problem in Ganeti and questioner should read archive.
So I wonder if Ganeti solved in some creative way or just ignored the problem? I'm especially interested in setups with only two nodes.
I think I founded answer for my question - Ganeti has only manual failover. Fencing is only needed in case of automatic failover to prevent concurrent access to the same resource (since in case of split nodes with quorum can't be sure if other nodes are dead ore there is only communication problem - STONITH), but in case on manual failover you relay on admins's judgement.
Maciek, you're correct, Ganeti only provides manual failover. With the
oob
framework we have the basic capability to do STONITH (via integration with a site-local framework; see internal documentation at docs.ganeti.org), but we have not yet extended this to automatic failover.