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LAN Interconnect VS Memory Channel interconnect

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Trusted Contributor

LAN Interconnect VS Memory Channel interconnect

We have a few Alpha machines and we are turning them into a Trucluster. The machines came with Gigabit Ethernet adapters, so we build the cluster with a LAN InterConnect. No problems.

Now people try to convince me that using MemoryChannel is the way to go. Faster, better and (something about) shared cluster memory for the better applications.

Is LAN I.C. really so much worse than M.C.?
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Honored Contributor

Re: LAN Interconnect VS Memory Channel interconnect

lan interconnect is slower but you can connect much more cluster members. memory channels are limited in the number of members. There are also some configuration restrictions as described in the cluster hardware installation guide.


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Trusted Contributor

Re: LAN Interconnect VS Memory Channel interconnect

So from the application point of view there is no difference?

They both offer the same functionality, but the way of doing it is different. Is this correct?
Watch, Think and Tinker.
Honored Contributor

Re: LAN Interconnect VS Memory Channel interconnect


If short application failover timing (in case of member HW failures)is important then you should consider memory channel interconnect.
With a LAN interconnect the cluster transition CNX-checking thats going-on to determine that a member is really gone may take up to 20 secs.

If the applications are in the realm of highperf tech parallel number crunching then the presence of the MC-API is a benefit.

For commercial applic's the performace difference with 1000Mb LAN is aro 9% in favor of memory channel.

JB.

_JB_
Honored Contributor

Re: LAN Interconnect VS Memory Channel interconnect

from application view there is no difference.
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Honored Contributor

Re: LAN Interconnect VS Memory Channel interconnect

I beg to disagree.

From an application point of view there can be a tremendous difference... notably if that application is ORACLE RAC.

MC and GB have comparable throughput of, for simplycity sake 100MB/sec... for large packets. The latency picture for MC is a lot better than GB. I forget the actual numbers but something like the GB being more close to 100 microsecond and MC close to 10 microsecond.

This becomes noticable with ORACLE RAC where the cluster interconnect is used for many short packet while lantency being critical (as users are being blocked). Now Oracle RAC also uses the Cluster interconnect for its 'cache fusion' where it ships database blocks and where bandwith become the dominant requirement.

[fwiw... Tru64 engineering was considering (had implemented, but will not ship) a transparant hybrid solution where the RDG services (reliable datagram) woudl decide on request datasize which communication channel to take. The best of both worlds! ]

Hein.
Respected Contributor

Re: LAN Interconnect VS Memory Channel interconnect

I had operational stability issues running memory channel on Tru64 5.1. If you only have the nodes connected to a singe memory channel hub, and something happens to one of the nodes, I found that it was hanging the entire cluster. This however did not happen if I reconfigured the MC adapters to run in Virtual hub mode.

The other way that I got around the problem was to rent a second memory channel hub, so that there was not a SPF on the interconnects. Personally, this proved to expensive for me.

I got on much better with Ethernet interconnects. I think there was also some discussion over small traffic(64K or smaller) being sent via ethernet node to node instead of via MC(if you had one implemented). I dont know if this would make any difference to you.

Since I have implemented LAN interconnects I have had no crashes or panics, compaired to MC for which I had to have numerous calls to HP for replacement MC adapters, additional hubs,sending binary.errlog,etc.

IMHO in terms of ease of implementation i prefer LAN

Trusted Contributor

Re: LAN Interconnect VS Memory Channel interconnect

So MC2 (Memory Channel v2) is better for the application, less latency. No problem MC2 wins.

But another issue is that MC2 is only supported up to 3km (6km with MC hub(s))

Seeing the current development of Gigabit ethernet, i think its safe to assume that Gigabit will soon win on the latency/distance/price front.

Ofcourse i cant see in to future, but its kind of hard to tell people what kind of path to take these days.

Watch, Think and Tinker.
Honored Contributor

Re: LAN Interconnect VS Memory Channel interconnect

Have a look into the roadmap of Alpha/Tru64 - maybe that kind of development will be honored with Itanium and HPUX!
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