NoDiskConflict when mounting GDE disk in read-only mode - google-compute-engine

Question

As previously reported here, two pods can't mount the same disk even though one of them tries to do it as read-only mode.
This is supposed to be allowed from Kubernetes documentation.
Mounting scheme is:
UniqueCluster/PodA has successfully mounted gdeDisk1 as read-write
UniqueCluster/PodB fails to start when mounting gdeDisk1 as read-only
Node description:
Name: gke-zupcat-cluster-8fd35d81-node-1zr4
Labels: kubernetes.io/hostname=gke-zupcat-cluster-8fd35d81-node-1zr4
CreationTimestamp: Wed, 22 Jul 2015 14:47:56 -0300
Conditions:
Type Status LastHeartbeatTime LastTransitionTime Reason Message
Ready True Thu, 23 Jul 2015 12:06:18 -0300 Wed, 22 Jul 2015 22:53:34 -0300 kubelet is posting ready status
Addresses: 10.240.17.72,146.148.79.174
Capacity:
cpu: 2
memory: 7679608Ki
pods: 40
Version:
Kernel Version: 3.16.0-0.bpo.4-amd64
OS Image: Debian GNU/Linux 7 (wheezy)
Container Runtime Version: docker://Unknown
Kubelet Version: v1.0.1
Kube-Proxy Version: v1.0.1
PodCIDR: 10.108.0.0/24
ExternalID: 11953122931827361742
Pods: (5 in total)
Namespace Name
default fastrwdiskpod-yu517
kube-system fluentd-cloud-logging-gke-zupcat-cluster-8fd35d81- node-1zr4
kube-system kube-dns-v8-i3h20
kube-system kube-ui-v1-8zdrq
kube-system monitoring-heapster-v5-e1zmi
No events.
Products versions:
Client Version: version.Info{Major:"1", Minor:"0", GitVersion:"v1.0.0", GitCommit:"cd821444dcf3e1e237b5f3579721440624c9c4fa", GitTreeState:"clean"}
Server Version: version.Info{Major:"1", Minor:"0", GitVersion:"v1.0.1", GitCommit:"6a5c06e3d1eb27a6310a09270e4a5fb1afa93e74", GitTreeState:"clean"}
docker version Docker version 1.7.1, build 786b29d

Answer 1

According to the GCE persistent disk documentation: "if you attach a persistent disk to multiple instances, all instances must attach the persistent disk in read-only mode."
The Kubernetes documentation for GCE PD volumes also explains this limitation: "A feature of PD is that they can be mounted as read-only by multiple consumers simultaneously. This means that you can pre-populate a PD with your dataset and then serve it in parallel from as many pods as you need. Unfortunately, PDs can only be mounted by a single consumer in read-write mode - no simultaneous readers allowed."