问题
What is the difference between persistent volume (PV) and persistent volume claim (PVC) in Kubernetes/ Openshift by referring to documentation?
What is the difference between both in simple terms?
回答1:
PVC is a declaration of need for storage that can at some point become available - as in bound to some actual PV.
It is a bit like the asynchronous programming concept of a promise. PVC promises that it will at some point "translate" into storage volume that your application will be able to use, and one of defined characteristics like class, size, and access mode (ROX, RWO, and RWX).
This is a way to abstract thinking about a particular storage implementation away from your pods/deployments. Your application in most cases does not need to declare "give me NFS storage from server X of size Y"; it is more like "I need persistent storage of default class and size Y".
With this, deployments on different clusters can choose to differently satisfy that need. One can link an EBS device, another can provision a GlusterFS, and your core manifests are still the same in both cases.
Furthermore, you can have Volume Claim Templates defined in your deployment, so that each pod gets a reflecting PVC created automatically (i.e., supporting infrastructure-agnostic storage definition for a group of scalable pods where each needs its own dedicated storage.
回答2:
From the docs
PVs are resources in the cluster. PVCs are requests for those resources and also act as claim checks to the resource.
So a persistent volume (PV) is the "physical" volume on the host machine that stores your persistent data. A persistent volume claim (PVC) is a request for the platform to create a PV for you, and you attach PVs to your pods via a PVC.
Something akin to
Pod -> PVC -> PV -> Host machine
回答3:
A Persistent Volume Claim is telling you what options you have access to in a particular cluster and they got this circular at this store called Smart Tech with some ads about your configuration options, those ads are the Persistent Volume Claim.
Inside your config file you write out the different Persistent Volume Claims that you are going to have inside your cluster, kind of like your wish list to Santa, but of course you are going to go take that to the sales guy at Smart Tech when you are done.
So you write a config file that says there should a 600gb hard drive option available to all your clusters and a 1TB hard drive option as well.
When you choose one of these options of the Persistent Volume Claim you go and request that Kubernetes (the sales guy) goes and gets that option for you, the option you have chosen, Kubernetes has to look through these instances of storage options in the stock room that are readily available. These instances of hard drives can be used right away and they are considered statically provisioned because they are created ahead of time.
On the other hand, there is dynamically provisioned options that were created on the fly, when you asked Kubernetes the sales guy, so kind of like just-in-time production, it got created when you immediately asked for it.
So the Persistent Volume Claim is the stores advertisement of options and whichever one you choose Kubernetes will go get it, either one in storage or create one on the fly.
The Persistent Volume is the actual product or options that you get back from Kubernetes that you asked for. If Kubernetes does not have what you asked for it will try to create it on the fly for you.
So the PVC is what Smart Tech is advertising they have to offer to your cluster which Kubernetes the sales guy will get for you and the PV is the actual finished product delivered to you.
来源：https://stackoverflow.com/questions/48956049/what-is-the-difference-between-persistent-volume-pv-and-persistent-volume-clai