Describe the bug

Volume stuck in attaching when creating from a raw type backing image. The same step works as expected for the qcow2 type.

To Reproduce

Steps to reproduce the behavior:

Using UI:
1. Create volume-1 with 3 replicas.
2. Create a backing-image from  volume-1 using `Export from a Longhorn volume` and `raw` .
3. Create volume-2 with 3 replicas using backing-image.
4. Attach volume-2.

Expected behavior

Should attach.

Log or Support bundle

time="2021-12-20T04:05:51Z" level=warning msg="Backing Image: invalid state starting after processing" component=backing-image expectedChecksum=50173936f83822c28812ea23f7f843a27e8b85f65626cbc339cea0e63aa770809f932343af9e6a0cd26bfa490d6d1928f19cf529ebd1e76ef74264fda961f810 name=b1 senderManagerAddress="10.30.1.84:8000" size=52428800 uuid=e779b2d5 workDir=/data/backing-images/b1-e779b2d5

Environment

• Longhorn version: master
• Installation method (e.g. Rancher Catalog App/Helm/Kubectl): kubectl
• Kubernetes distro (e.g. RKE/K3s/EKS/OpenShift) and version:
  • Number of management node in the cluster:
  • Number of worker node in the cluster:
• Node config
  • OS type and version: sles15-sp3
  • CPU per node:
  • Memory per node:
  • Disk type(e.g. SSD/NVMe):
  • Network bandwidth between the nodes:
• Underlying Infrastructure (e.g. on AWS/GCE, EKS/GKE, VMWare/KVM, Baremetal):
• Number of Longhorn volumes in the cluster:

Additional context