Cannot connect to Pool Master by using XenCenter. XenCenter gives an error message:
Unable to connect to server '10.90.206.83'.
Could not find XenServer on '10.90.206.83'.
Check that XenServer is configured correctly on '10.90.206.83 and try again.

However, Pool Master is accessible by SSH. The command df shows that the root disk /dev/sda1 is full:

[root@XenServer01 ~]# df -h 
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             4.0G  4.0G     0 100% /

Complete the following steps:

1. Cleanup some space from root disk filesystem
2. Reboot system to clean deadbeef domains.
3. Apply recommended hotfixes and driver disk updates

Problem Cause

deadbeef domains and root disk filesystem was full.
XenServer was not able to connect to XenCenter because the XAPI service cannot start when the filesystem is full.