general question on volume shadowing

[Uwe Zessin]

Jan,
excuse me for being a sceptical one ;-)

Have you had practical experience with this? If I recall correctly the capability to do a failover between MSCP served fibre paths and local paths isn't that old (V7.3?).

[Jan van den Ende]

Uwe:

Yes, we started doing this when we moved form HSZ40's to HSG80's.
Our (I guess famed by now) cluster works this way since last juny.

Jan

[Jan van den Ende]

Oh, and yes Uwe, it was introduced at 7.2-2 (which we skipped, at 7.3-1 now and evaluating 7.3-2)

Jan

[Uwe Zessin]

Ah, thank you. I have been in a project with VMS V6.2-1H3 quite some years ago where the customer had two HS211(?)-based FDDI storage servers and the missing direct paths to all devices made the handling 'quite interesting'.

It was the second cluster implementation for the software vendor and the customer had even less experience. The hardware was already ordered, but it was still an interesting project.

[Keith Parris]

The ability to fail over between direct Fibre Channel (snd SCSI) paths and MSCP-served paths was introduced in 7.3-1, and is NOT available in 7.2-2. (A number of features from 7.3 were included in 7.2-2, but 7.3-1 came out later.)

References:

7.2-2 New Features Manual: http://h71000.www7.hp.com/doc/722final/6650/6650pro.html

7.3-1 New Features Manual: http://h71000.www7.hp.com/doc/731FINAL/6657/6657PRO.HTML

"Multipath failover to an MSCP-served path for disks is implemented in SCSI and Fibre Channel configurations."

[Jan van den Ende]

keith, I must stand corrected.

I know I read SOMETHING on this kind of stuff in the new shadowing manual that came with 7.2-2, but since we never used it, I never went deep into the details.
7.2-2 only introduced fiber channel storage, and I got them confused.

Sorry for the misinformation.

Jan

[Keith Parris]

Jan, you were probably thinking of all the new DCL commands added in support of shadowing in Fibre Channel-based DT clusters so folks could do their best to limp by until failover to/from MSCP-served paths could be delivered in 7.3-1. There was a big white paper written about the topic at the time -- you can still find that via http://h71000.www7.hp.com/openvms/fibre/index.html

From the 7.2-2 release notes:
"Disaster-tolerant support for host-based volume shadowing in an OpenVMS Cluster configuration using shared Fibre Channel storage
- This support gives system managers greater control for managing failover.
- This feature is included in OpenVMS Version 7.3 and is also provided in Volume Shadowing update kits for OpenVMS Alpha Version 7.2-1H1 and for OpenVMS Alpha Version 7.2-1.
- The support provided in this release is identical to that provided in OpenVMS Version 7.3."

In retrospect, failover with these commands ended up being so complicated, messy, and error-prone that I ended up recommending that folks simply avoid connecting up their inter-site Fibre Channel link (thus forcing the use of only an MSCP-served path to remote disks, and obviating any failover issues) until they could get to 7.3-1.