XenServer Administrator's Guide 4.1.0

XenServer Hosts
and resource pools
8
When a member XenServer Host fails, there may be VMs still registered in the running state. If you are sure
that the member XenServer Host is definitely down, and that the VMs have not been brought up on another
XenServer Host in the pool, use the xe vm-reset-powerstate CLI command to forcibly halt the VMs. See
Section 5.4.22.21, “vm-reset-powerstate” for more details.
2.7.2. Master failures
Every member of a resource pool contains all the information necessary to take over the role of master if
required. When a master node fails, the following sequence of events occurs:
1. The members realize that communication has been lost and each retry for sixty seconds
2. Each member then puts itself into emergency mode, whereby the member XenServer Hosts will now
accept only the pool-emergency commands (xe pool-emergency-reset-master and xe pool-emergen-
cy-transition-to-master).
If the master comes back up at this point, it will reestablish communication with its members, they will leave
emergency mode, and operation will return to normal.
If the master is really dead, though, you should choose one of the members and issue to it the command
xe pool-emergency-transition-to-master. Once it has become the master, issue the command xe pool-
recover-slaves and the members will now point to the new master.
If you repair or replace the server that was the original master, you can simply bring it up, install the XenServ-
er Host software, and add it to the pool. Since the XenServer Hosts in the pool are enforced to be homoge-
neous, there is no real need to make the replaced server the master.
When a member XenServer Host is transitioned to being a master, you should also check that the default
pool storage repository is set to an appropriate value. This can be done using the xe pool-param-list
command and verifying that the default-SR parameter is pointing to a valid storage repository.
2.7.3. Pool failures
In the unfortunate event that your entire resource pool fails, you will need to re-create the pool database from
scratch. Be sure to regularly back up your pool-metadata using the xe pool-dump-database CLI command
(see Section 5.4.11.2, “pool-dump-database”).
Procedure 2.9. To restore a completely failed pool
1. Install a fresh set of hosts, and apply your Enterprise Edition license to them. Do not pool them up
at this stage.
2. For the host nominated as the master, restore the pool database from your backup via the xe pool-
restore-database (see Section 5.4.11.8, “pool-restore-database”) CLI command.
3. Connect to the master host via XenCenter and ensure that all your shared storage and VMs are avail-
able again.
4. Perform a pool join operation on the remaining freshly installed member hosts, and start up your VMs
on the appropriate hosts.
2.7.4. Coping with Failure due to Configuration Errors
If the physical host machine is operational but the software or host configuration is corrupted: