Re: White paper: CHARON-VAX cluster w/ shared SCSI disks

From: Wilm Boerhout (wboerhoutOLD_at_PAINTvxcompany.com)
Date: 10/12/03 

Date: Sun, 12 Oct 2003 21:44:18 +0200

Look at the picture in the white paper. The SCSI box has a multipoint
controller -and some internal redundancy as well-. I connect two VMS
hosts (well, CHARON-VAX emulated hosts) using CHARON-VAX's ability to
connect to physical SCSI disks, bypassing Windoze disk device drivers
altogether.

More graphical: from the >>> boot prompt on one (emulated) VAX, you see
all SCSI disks (but not the other VAX host). From the other VAX host's
boot prompt you see those same SCSI disks (but not the first host). So,
for all practical purposes, the VAXen share the SCSI disks. They look
the same, they have the same names, so let's assume they are the same :-)

You need the VMS lock manager of course to ensure the integrity of the
I/O to / from the disks. Windoze (sort of in between, but not very much
so with CHARON-VAX) knows absolutely nothing about synchronizing I/O on
these same disks. You need VMS clusters to do that.

In fact, I like to think it's more like DSSI than shared SCSI on Alpha,
but it's not the same. It works -has been running for days with all
kinds of loads- not only by haphazard operational luck, but by
VAXcluster architectural design as well. Of course, the VAX cluster SPD
will not be rewritten because of this.

Is it a bird? Is it a plane? It's... it's... it's a VAXcluster! We hope
to have one on line before long so the community can take a look at it
from the inside.

H Vlems wrote:

> Wilm,
>
> you've got me thoroughly confused by now. A shared SCSI cluster has at least
> one SCSI bus with two VMS hosts attached to the bus (those buses). The data
> travels the SCSI bus(es) the lockmanager uses, by default, the fastest
> common NI it can lay its hands on.
> AFAIK Charon is an emulator that runs on a Windows platform and shared SCSI
> (with both windows hosts at work) just does not exist. IMO there's no such
> thing as a simulated shwared SCSI bus :-)
>
> So obviously I missed something, somewhere, but what ?
>
> hans
> "Wilm Boerhout" <wboerhoutOLD@PAINTvxcompany.com> schreef in bericht
> news:bmc8ae$e0t$1@reader11.wxs.nl...
>
>>But Hans, in this setup, the data *does* travel on the SCSI bus. The
>>lock manager traffic user the network interconnect.
>>
>>Robert Lyons naming it "Mixed Interconnect"is right in that respect.
>>That is exactly why we demonstrated it. Please read the setup in hte
>>white paper, and judge for yourself.
>>
>>I may not have been clear enough in my description, please comment so
>>that it can be made clear.
>>
>>Wilm
>>
>>H Vlems wrote:
>>
>>>Wilm
>>>
>>>if you describe your set up as a "SCSI cluster" (with or without the
>
> prefix
>
>>>shared) most people in this newsgroup will translate that as a VMS
>
> cluster
>
>>>where data travels a shared SCSI bus. Whatever way you may want to put
>
> it,
>
>>>for VMS system managers the Charon setup is a straight forward NI
>
> cluster.
>
>>>Which incidentally may also be achieved if you run simh.
>>>
>>>Hans
>>>
>>>"Wilm Boerhout" <w.boerhoutOLD@PAINTplanet.nl> schreef in bericht
>>>news:bmbn9m$lml$1@reader11.wxs.nl...
>>>
>>>
>>>>Thanks Rob, I will keep this channel open for a few weeks and then write
>>>>a version 1.1.
>>>>
>>>>As for the naming, the "Guidelines for OpenVMS Cluster Systems" manual
>>>>speaks of a "SCSI multihost OpenVMS Cluster" where Alpha systems are
>>>>concernd. So, maybe a "SCSI multihost OpenVMS VAXcluster" would be
>>>>appropriate? I like your suggestion of "Mixed Interconnect" as well.
>>>>
>>>>Rob Lyons wrote:
>>>>
>>>>
>>>>>Thanks for getting the word out to the rest of us who were not able to
>>>
>>>attend the Dutch Technical Update Days.
>>>
>>>
>>>>>I suggest the name for your configuration is LAVC with shared SCSI or a
>>>
>>>Mixed Interconnect Cluster since the interconnect that
>>>
>>>
>>>>>carries the cluster traffic names the cluster type, by convention. The
>>>
>>>term "SCSI-cluster" incorrectly implies that the SCSI bus is
>>>
>>>
>>>>>carrying SCA cluster traffic.
>>>>>
>>>>>Be wary of using the 100Mb Ethernet setting for the NI speed. In
>>>
>>>clusters we've built on the other side of the pond, activities as
>>>
>>>
>>>>>simple as disk to disk copy between clusters can swamp the NI and cause
>>>
>>>the cluster to become unstable. The 10Mb setting avoids
>>>
>>>
>>>>>that pitfall.
>>>>>
>>>>>Shared SCSI has a very limited number of configurations possible due to
>>>
>>>the cable length restrictions of SCSI. The best way we have
>>>
>>>
>>>>>found to build scalable clusters is to use Fibre Channel. The same PK
>>>
>>>port driver is used for SCSI and Fibre Channel and the
>>>
>>>
>>>>>performance profile with an HSG80 or MSA1000 storage controller is
>>>
>>>impressive.
>>>
>>>
>>>>>As you find additional hints and kinks, keep the information flowing.
>>>
>>>The community at large all benefit from your efforts.
>>>
>>>
>>>>>Rob Lyons
>>>>>Resilient Systems Inc.
>>>>>w-w-w.resilientsys.com
>>>>>
>>>>>
>>>>
>>>>--
>>>>Wilm Boerhout
>>>>
>>>>w.boerhoutOLD@PAINTplanet.nl
>>>>
>>>>remove OLD PAINT from reply address first
>>>>*** my opinions are strictly my own ***
>>>>
>>>
>>>
>>>
>>--
>>Wilm Boerhout
>>VX Company, The Netherlands
>>
>>wboerhoutOLD@PAINTvxcompany.com
>> (remove OLD PAINT from reply address)
>>
>>*** my opinions are strictly my own ***
>>
>
>
> 

-- 
Wilm Boerhout
VX Company, The Netherlands
wboerhoutOLD@PAINTvxcompany.com
  (remove OLD PAINT from reply address)
*** my opinions are strictly my own ***

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