VDSM copy functions with preallocated disks cause severe slowdowns on NFS v3 storage domains

Solution In Progress - Updated -

Issue

  • Performing a data copy function of a preallocated volume, such as creating a template, results in a slowdown of all i/o to/from the NFS server in question. The NFS file systems are V3, with the default mount options provided by RHV.

  • On the SPM host, MiscFileReadException read timeouts in VDSM and high repoStats 'delay' times are seen, Storage Domains become 'INVALID', and VM's become unresponsive.

  • All storage domains on the same NFS server are affected.

  • This can be replicated by manually running;

  # qemu-img convert -p -t none -T none -f raw <src path> -O raw -o preallocation=falloc <dest path>
  • Removing "-o preallocation=falloc" circumvents the problem, but the result is a sparse file instead of a preallocated file.

Environment

  • Red Hat Virtualization (RHV) 4.3.9
  • Red Hat Virtualization Hypervisor (RHVH) 4.3.9;
    • vdsm-4.30.44-1.el7ev.x86_64
    • libvirt-4.5.0-33.el7.x86_64
    • qemu-kvm-rhev-2.12.0-44.el7.x86_64
    • ioprocess-1.3.1-1.el7ev.x86_64
  • NFS v3 storage domains

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