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The Inhibitors To I/O Virtualization

In my entry "I/O Virtualization: When, Not If," I discussed some of the merits of I/O Virtualization (IOV) and the
value in offloading I/O responsibilities from the hypervisor with
SR-IOV (single route IOV). While SR-IOV and IOV may seem like great strategies, there are
some inhibitors that need to be overcome. The first is OS or hypervisor
support, and the second is dealing with the disruptions to the network
and storage infrastructure when first implemented.

When it comes to SR-IOV enabled cards, the primary challenge is when will the operating systems and hypervisors support the
technology? To take advantage of all that SR-IOV has to offer, this
support needs to be there. As we discussed, IOV gateways (IOG) in large
part solve this problem by presenting SR-IOV cards as "regular" cards to
the servers that attach to them. Vendors may forgo SR-IOV altogether
and develop their own multi-host cards for their gateways, so they don't
have to wait for OS, hypervisor support or SR-IOV itself. They will have
to develop the card itself, and potentially a OS driver, or
require an IOG.

If the IOG is the way to go, then the bigger challenge is implementing
IOG itself. As we discussed in our article "What is I/O Virtualization"
this is infrastructure and the gateway device does need to be in
between the storage, the networks and the servers they are connecting
to. Partly, this is just a reality of infrastructure where changes are
slow to take place. Certainly steps can be taken to minimize downtime
associated with implementing the IOG by leveraging the existing high
availability in the environment. The change over to the IOG can be made
one link at a time.

The other inhibitor to IOV goes beyond the speed at which infrastructure
changes, though. Some of the initial forays into the I/O market
compounded the problem by introducing a new type of card that is
installed in the server and a new connection methodology from the server
to the gateway. Often this was either PCIe or Infiniband. While the I/O
performance of these solutions was ideal, it did involve installing a
new class of connection into the environment. For some servers it is
reasonable to assume they needed the advanced I/O performance of these
technologies, but for many others it did not. What was needed was a less
disruptive way to bring IOV to servers with more modest I/O

The next step in IOV is to leverage a connection technology that is
already widespread in the data center. Ethernet is the most
likely candidate. While today it would be limited to a 10GbE connection
speed, over the next few years that will increase significantly. The
advantage of leveraging Ethernet is that the infrastructure is already
in place, and the move to 10GbE is already happening in many servers. As
the administrators are installing 10GbE cards, why not also pick one that
can support IOV? This will allow maximum flexibility when dealing with
the I/O demands placed on the infrastructure by server virtualization as
well as give flexibility when choosing future storage and network
protocols. Moving to Virtualized I/O can be somewhat disruptive, choosing the right
time to make that move makes it less so. The right time may very well
be as you upgrade the environment to 10GbE.