Re: [PATCH 0/3] virtio-blk: support zoned block devices

[Dmitry Fomichev <Dmitry.Fomichev@wdc.com>]

On Tue, 2022-09-20 at 06:41 -0400, Stefan Hajnoczi wrote:
> On Tue, 20 Sept 2022 at 03:43, Christoph Hellwig <hch@infradead.org> wrote:
> > 
> > On Sun, Sep 18, 2022 at 10:29:18PM -0400, Dmitry Fomichev wrote:
> > > In its current form, the virtio protocol for block devices (virtio-blk)
> > > is not aware of zoned block devices (ZBDs) but it allows the driver to
> > > successfully scan a host-managed drive provided by the virtio block
> > > device. As the result, the host-managed drive is recognized by the
> > > virtio driver as a regular, non-zoned drive that will operate
> > > erroneously under the most common write workloads. Host-aware ZBDs are
> > > currently usable, but their performance may not be optimal because the
> > > driver can only see them as non-zoned block devices.
> > 
> > What is the advantage in extending virtio-blk vs just using virtio-scsi
> > or nvme with shadow doorbells that just work?
> 
> virtio-blk is widely used and new request types are added as needed.
> 
> QEMU's NVMe emulation may support passing through zoned storage
> devices in the future but it doesn't today. Support was implemented in
> virtio-blk first because NVMe emulation isn't widely used in
> production QEMU VMs.
> 
> Stefan
 
A large share of hyperscaler guest VM images only supports virtio for
storage and doesn't define CONFIG_SCSI, COPNFIG_ATA, etc. at all in their
kernel config. This is especially common in hyperscale environments that
are dedicated to serverless computing.

In such environments, there is currently no way to present a zoned device
to the guest user because the virtio-blk driver is not ZBD-aware. An attempt
to virtualize a host-managed drive in this setup causes the drive to show up
at the guest as a regular block device - certainly not an ideal situation.

Dmitry