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

John R Pierce pierce at hogranch.com
Thu Sep 16 02:24:27 EDT 2010

  On 09/15/10 2:19 AM, Rudi Ahlers wrote:
> Hi all,
> I'm just curios and would like some input from the community on this
> one. We're busy budgeting for a couple of new servers and I thought it
> would be good to try out the Core i7 CPU's, but see the majority of
> them don't offer VT-d, but just VT-x. Looking at the LGA1366 range,
> only the "Intel lga1366 i7 980XE" (from the list of what our suppliers
> stock) have VT-d, and it costs 4x more than "Intel lga1366 i7 930" or
> 2x more than "Intel lga1366 i7 960". From a budget perspecitve I could
> purchase 4 more CPU's, which could translate to 40x - 80x more VM's
> being hosted for the same capital outlay. Experience has shown that we
> under-utilize CPU's by a great margin and memory / HDD IO is our
> biggest bottleneck on any server.
> So, if VT-d really necessary?
> We mainly host XEN virtual machine for the hosting industry, i.e. we
> don't need / use graphics rendering inside VM's, or need DAS on the
> VM's, etc.

Core I7 is the branding for the desktop CPU family.  The Server 
processors are branded Xeon 5500 and 5600 (for dual socket servers) and 
Xeon 7000 for 4+ socket servers.   Typically, desktop processors go with 
desktop motherboards which don't support ECC memory, probably don't have 
remote management features, likely don't readily support redundant 
power, and often have only a single NIC onboard.  A server board will 
likely have significantly more IO bandwidth, oriented towards network 
and disk IO rather than graphics.

IMHO, the dual socket 5600 family is the sweet spot of price/performance 
for a VM host, with 2 x 6 cores, and typically 12 memory slots (2x3 per 
CPU).  populate the memory with 6 matching DIMMs for best performance.

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