Support creating a blank VHD in a storage account

[colemickens]

There are Kubernetes scenarios where users need to be able to provision blank VHDs in a storage account so they can make them available in their cluster.

Today, basically there are only two options as far as I can tell:

1. Attach a new blank disk to a VM from the Portal or CLI. Immediately detach the disk. At least it's a valid VHD.
2. Create the VHD on your local system. (qemu-img, etc)

There ought to be a way to do this from CLI (or better yet, if this were something that Storage could do via an API).

[rootfs]

Though it is possible to use a combination of PutPageBlob and PutPageb to create a blank page blob and then append a VHD label to the blob, an Azure API support is ultimate the best idea for the following reason:

• it is atomic operation
• Even if VHD format changes, the API won't change.

[ahmetb]

Here's a sample piece of code: https://gist.github.com/sedouard/0468d1b2d0153ca9a652

But ideally this problem should be resolved with upcoming new Disks APIs.

[jpoon]

One such user scenario is Pachyderm which requires a data-disk to be created and mounted to be used for their RethinkDB (pachyderm/pachyderm#960) and having an API to create a blank data-disk would be da 💣 or...at least put Azure on par with AWS and GCE:

AWS: aws ec2 create-volume ...
GCE: gcloud compute disks create ...

[jpoon]

I ended up wrapping Steven Edouard (@sedouard)'s workaround into a "helper" Docker image (https://github.com/jpoon/azure-create-vhd). Still would be good to have this in the Azure CLI.

[colemickens]

I had already done that as well, for the azure-kubernetes-demo repo that shows how to use data disks: https://github.com/colemickens/azure-tools

Mine can preformat as well, and create storage account/containers if they're missing.

[dbalaouras]

Is there any update on this? Cole Mickens (@colemickens) docker image works good, but enabling this operation via the Azure CLI is really the way to go.

[colemickens]

No update here. When everything moves to managed disks, there will be an easy way to do this, including CLI support. For now, the non-managed disks implementation simply has no API for disk creation.

For now, it's much easier to just use dynamic provisioning... you just create a PVC for whatever size you want and Kubernetes will make the PV for you.

[dbalaouras]

Cole Mickens (@colemickens) I managed to use dynamic provisioning via the kubernetes.io/azure-disk Provisioner but I'm hitting the very low limit (i.e. 4) of mounted disks on my A2 VM.

Is there a way to do the same dynamic provisioning with azure-file? I.e., dynamically create files in my Storage Account and mount them on my Pods.

ta.

[colemickens]

Dynamic provisioning for Azure Files should be in 1.7, and probably cherry-picked to 1.6.1, I think: kubernetes/kubernetes#42170

But you probably shouldn't use it for anything serious at all. The perf is definitely not good enough for a DB or anything.

[dbalaouras]

Cole Mickens (@colemickens) thx for the prompt response. And yeah, I recon azure-files are SMB drives and not suitable for DBs. Wondering if it could work for a small SQLite though..

In any case, do you happen to know why is there a limitation on the number of vhds I can mount on a VM and why is it so low?

{
    "maxDataDiskCount": 4,
    "memoryInMb": 3584,
    "name": "Standard_A2",
    "numberOfCores": 2,
    "osDiskSizeInMb": 1047552,
    "resourceDiskSizeInMb": 138240
  }

[colemickens]

That's just how Azure sells their SKUs. I'd suggest contacting support to ask them and express your interest in different SKUs with lower compute and more disks.

[dbalaouras]

Thx Cole Mickens (@colemickens).