Does Ubuntu PPC64 14.04 LTS support the dual disk I/O path provided by dual VIO servers on IBM power8 systems?
Alternatively, is it wise to install this server with storage provided by just a single VIO server?
Does Ubuntu PPC64 14.04 LTS support the dual disk I/O path provided by dual VIO servers on IBM power8 systems?
Alternatively, is it wise to install this server with storage provided by just a single VIO server?
The multipath packages are included in Ubuntu 14.04 LTS for ppc64el as well, which handle the dual VIOS scenario (as well as Fibre Channel, and IPR controllers w/ multipath capability)
See Ubuntu Help, 14.04 LTS (Server column), DM-Multipath, sections "Setting up DM-Multipath Overview" then "DM-Multipath Setup Overview", and "Device Mapper Multipathing" then "Installing with Multipath Support".
Basically, either:
disk-detect/multipath/enable=true option in the kernel command line; or multipath-tools-boot package (this installs the multipath-tools package automatically).Note: On option 2, some users had boot problems (LP bug) if not using user_friendly_names (which is enabled by default on option 1). 
You can enable it before installing multipath-tools-boot with this command:
$ cat <<EOF | sudo tee -a /etc/multipath.conf
defaults {
    user_friendly_names yes
}
EOF
If you enabled it after installing multipath-tools-boot, just update the initramfs; for example:
$ sudo update-initramfs -u
I would add that you should look at running three VIOS. This would allow you to upgrade or service a VIOS without exposure. I would never run on one VIOS as they sometimes do go down from hardware and software issues. This just based on my experience with PowerVM in very large configurations.