Re: [Xen-users] XCP, NFS for storage and bonded NICs

[Craig Miskell <craig.miskell@xxxxxxxxxx>]

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Bart Coninckx wrote:
> On Monday 01 November 2010 00:30:52 Craig Miskell wrote:
>> Hi,
>>      Is it possible to gain any speed advantage out of bonded NICs at the XCP
>> host end, when accessing a single NFS Storage Repository?
>>
>> As I understand most bonding mechanisms, they use MAC addresses, or at best
>> IP addresses and port numbers, as input to the hash to decide which link
>> to use for a given packet.  Which means that all traffic between a given
>> host and the NFS server will hash to the same value every time, and go
>> over just one link.
>>
>> Have I some obvious (or not so obvious) trickery or options?
>
> Somebody correct me if I'm wrong but if you use the same switch to get to the 
> NFS server, you need to pick the 802.3ad bonding and see to it that your 
> switch supports it.
Sure, that's given, but I'm not sure it answers my question.  Getting bonding
going isn't the issue, what I'm interested in is whether there's any tricks to
actually utilise both links from a host talking to just a single NFS storage
device.

To quote from http://en.wikipedia.org/wiki/802.3ad:

"When balancing traffic, network administrators often wish to avoid reordering
Ethernet frames. For example, TCP suffers additional overheads when dealing with
out-of-order packets. This goal is approximated by sending all frames associated
with a particular session across the same link[6]. The most common
implementations use L3 hashes (i.e. based on the IP address), ensuring that the
same flow is always sent via the same physical link."

So I guess I don't *want* to balance a single flow across multiple links.  So if
I want to balance NFS traffic across links I need more than one distinct TCP
connection to the NFS server, which I'd guess needs at least two distinct
mounted shares.  Is anyone doing anything like that?

Thanks,

- --
Craig Miskell
Senior Systems Administrator
Opus International Consultants
Phone: +64 4 471 7209
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