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

[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.)

> 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?



-- 
Grant. . . .
unix || die