[Info-vax] ES47 2G FC and rx2800 i4 8G FC in same VMS Cluster with Shadowsets on shared storage controller? Is this possible?

[Jan-Erik Söderholm]

Den 2020-03-15 kl. 13:17, skrev Jan-Erik Söderholm:
> Den 2020-03-15 kl. 00:02, skrev Grant Taylor:
>> On 3/14/20 4:26 PM, Colin Butcher wrote:
>>> Brocade FC switches implement 3 speeds: 1/2/4, 2/4/8, 4/8/16, and so on.
>>
>> Good to know.
>>
>>> You might be able to have cascaded switches in the same fabric to handle 
>>> a wider range of speeds, but you'll add latency due to the extra switch 
>>> hops
>>
>> Will the extra latency in and of itself be a problem?
>>
>>> and you could run into firmware interoperability issues.
>>
>> I would expect that these issues could be overcome.
>>
>>> The 16GigFC storage should run at 4GigFC (16/8/4), as should the 16GigFC 
>>> HBAs in the rx2800s, so that might work for you as part of a migration 
>>> design with your 4GigFC switches, changing over to faster switches later 
>>> once the Alphas are gone.
>>
>> Other than the added latency of cascading switches, what would be the 
>> downside of doing so?
>>
>> It seems to me like configuring all the new equipment on the 16 Gbps FC 
>> switch would be a one time operation.  Once the cluster is migrated from 
>> the Alphas to the Itaniums, the old Alphas, 4 Gbps FC equipment could be 
>> removed, leaving the new systems intact and not needing any further changes.
>>
>> What is the down side of doing this other than the extra latency? 
>> (Presuming that any firmware issues are null or overcome.)
>>
> 
> Our 2 GB AlphaServer DS20e (as far as I know, the max FC speed) runs in an
> environment where the Power9 and other "modern" servers uses 32 GB against
> the same IBM V7000 Storwize SAN systems. So we share SAN with other i/OS,
> AIX, Windows and Linux systems.
> 
> I know that they (the FC/SAN management group) have saved a few FC switches
> that supports 2 GB but I have little knowledge about how it is setup in
> the rest of the FC network.
> 
> If it could be valuable, I can check with the FC/SAN group about it
> and maybe get a setup description. That is, how are our 2 GB DS20s
> interfaced against the othervise 32 GB SAN system.
> 
> But, it does work very well. No FC issues since we switche to this setup
> 6-7 years ago. The SAN systems has moved from IBM D8000 to V7000 and there
> have been several on-line FC switch FW updates and also switch replacements
> with no interuptions on our (OpenVMS) side. Just the usual "Last switched
> to" and "Last switched from" counters on the "I/O Paths" (4 of them/disk).
> 
> And as far as I understand, all our OpenVMS storage is on SSD after the
> last IBM SAN hardware change.
> 
> 
>>> Fibrechannel is cut-through switching, not store and forward switching.
>>
>> How does Fibre Channel switching handle something coming in at 2 Gbps 
>> going out at 4 Gbps?  Is there any sort of buffering?  Does it go out the 
>> 4 Gbps interface at 2 Gbps?  Or does the FC switch do something to 
>> receive the entire frame (?term?) at 2 Gbps and then send it at 4 Gbps?
>>
> 
> I guess that traffic going DS20 -> SAN is no issue, it is just that the
> higher speed parts will not be saturated. We (the VMS) side can saturate
> our 2 GB line but the 32 GB line going in to the SAN will of course not
> saturate at 32 GB. It will still be a 32 GB line, but most of the time
> being idle/silent.
> 
> For traffic the other way (32 GB SAN -> 2 GB DS20) I guess that there must
> be some handshaking backwards so that the SAN will wait for the next switch
> to send to the slower line before pushing out the next 32 GB FC package.
> 
> And it is fast, we easily saturate the CPU before the storage I/O.
> A little depending on what we do (a SEARCH vs. an Rdb query), but still
> fast, when measured against the heydays of an 666 Mhz DS20...
> 
> 
>>
>>
> 

Got a reply from the SAN group.

All used FC switches supports 2/4/8/16 Gbs.
Don't know the brand or type of them.
The Alpha servers connects with 2 Gbs.
The SAN used (IBM V7000) only connects using 16 Gbs.
Most other modern (mainly IBM P9) systems use 16 Gbs.

FWIW...

Jan-Erik.