Resource Pool Member Host Types
Master pool member - single control point for all XS in the pool
- maintains configuration data
- manages distributed locking for shared storage
- configures secondary XS in the pool

Secondary pool members
- controlled through master
- maintains pool configuration backup
- can be promoted to pool master

Resource Pool Types
Homogenous pools
- same CPU, make, model and feature set
- same version and service pack level
Heterogeneous pools
- same CPU vendor family (AMD, Intel)
- CPUs must support Intel FlexMigration or AMD Enhanced Migration
- older CPU features must be a subset of the CPU features of the new XS joining pool
- XS Advanced edition or higher

XenMotion / Shared Configuration
- Access to the same shared storage
- Connected to the same network
- VM cannot migrated if: VM is on non-shared storage, connected to single server private network, XenServer tools not installed

Member failure
- HA enabled, another master server is automatically elected
- HA disabled, wait for master or manual new master promote
- Retry connection to master server for 1 minute
- Go into emergency mode if master remains unreachable
- Retry connection to master every 3-5 minutes
- Promote secondary to master commands: 
xe pool-emergency-transition-to-master
xe pool-recover-slaves
xe pool-param-list

vApps
- Logical grouping of one or more related VMs
- Managed as a single entity
- VMs within a vApp do not have to reside on the same XS host
- Start order (VMs with start order 0 will be started first)
- Attempt to start next VM after (delay interval between VM power on)