You ever got the following error when using the mkvdev command?

$ mkvdev -vdev hdisk69 -vadapter vhost10 -dev gzaix_120G_10
gzaix_120G_10 Available
To see the newly added disk, client partition needs reboot.

There is a page on IBM site which is explaining in detail why this is happening.
I will tell you the short version: check if the newly added disk is from the same storage type.
Meaning, if your existing disks assigned to the VIO's client are from e.g. DS8000 and the new one is from SVC, you will for sure get this error because they have different max_transfer speed:

SVC disk:

# lsdev -Cc disk | grep hdisk69
hdisk69 Available 01-00-02 MPIO FC 2145
# lsattr -El hdisk69grep max_transfer | awk '{print $2}'
0x40000

DS disk:

# lsdev -l hdisk11
hdisk11 Available 04-01-02 IBM MPIO FC 2107
# lsattr -El hdisk11 | grep max_transfer | awk '{print $2}'
0x100000

So, remove gzaix_120G_10 and create it with one disks with the same type. You could also create another vadapter for the same client and attach the SVC disks to it, keeping different types of disks separate.