[CentOS] is Intel VT-d "really" necessary?

Rudi Ahlers Rudi at SoftDux.com
Wed Sep 15 07:48:54 EDT 2010

On Wed, Sep 15, 2010 at 1:28 PM, Alexander Dalloz <ad+lists at uni-x.org> wrote:

> VT-d is not a necessity in general. It all depends on the kind of
> virtualization you run. If you run only paravirtualized guests on Xen,
> then there is not any need for VT-d (see [1]). If you fully virtualize for
> instance Windows guests, then specific systems may profit i.e. from a
> reserved network card by better network I/O.

ok, that's kinda what I thought as well. We don't use Windows VM's,
but rather dedicated Windows servers if needed.

> Whether VT-d is useful to have may too depend on whether pricing for the
> customer can be adjusted when providing such an extra feature.
> >From own experience I concur that often with most modern x86 architecture
> systems the I/O (network and storage) is the bottleneck in the area of
> virtualization.

That's what I found as well so I want to concentrate on better I/O
throughput. In general we don't saturate the 1GB NIC's. As soon as it
gets to a certain threshold, we move some of the VM's to a new server
instead. I guess I could look into dual / quad NIC bonding, but that
would mean downtime on the server while the NIC's are installed.

> Just curious, do you really run virtualization for hosting on systems with
> uni-processor design? I mean not choosing professional dual quad- or
> hexa-core processor systems with Nehalem / Westmere Xeon CPUs or their AMD
> Opteron counterpart?

Generally we use systems with 8cores+, i.e. Quad Core with HT, or dual
Quad Core with HT. But I want to see if I could use the money spend on
those expensive CPU setups more wisely with RAM & I/O.

> Regards
> Alexander
> [1] http://wiki.xensource.com/xenwiki/VTdHowTo
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Kind Regards
Rudi Ahlers

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