Alternate PV path mirror

[Sunny Chen]

Hi, guys:

I am using 2 Fibre card(A3404A) in a HP-UX 10.20 server, K580, they are both using FC-AL EMC frame, I am going to migrate the data to Fibre switch HITACHI, so I will install one Fibre card (A6685A) to hookup the HITACHI, and then do the mirror. Since we use alternate path for EMC, I have no idea what will happen for the mirror, if we only use one Fibre card for HITACHI, and what will happen for break the mirror, should I just simply mirror the "true" pv and forget those "alternate path"? I don't have any experience on this before, and I am using mirror-ux, very appreciate your help.

[Martin Johnson]

The alternate path should have no real effect on you mirroring. The alternate path is idle until you lose your primary path, then the alternate becomes the primary. Without the alternate path, losing the primary means you have lost communication with your disk (which means the data on this disk will become stale as far as the mirror in concerned).

HTH
Marty

[S.K. Chan]

The "alternate path" setup and "mirroring" are 2 separate thing. Having an alternate path in your volume group means if you have another route to the physical volumes if the primary path fails (example if one of the fiber card is faulty). That does not change the mirroring behavior of your volume group if those physical volumes (disks) are mirrored. Remember Mirror/UX is software mirroring, not hardware mirroring. If you use only one fiber card for the Hitachi, the only disadvantage is in the event of that card failed for some reason, you will not have an access to the volume group, that's all.

[Tim D Fulford]

I agree with the above....

Is the HITACHI a disk subsystem or a fiber switch? I'm not sure from your question?

If HITACHI is a Disk subsystem & you are migrating the data from EMC to HITACHI. Using Mirror/UX would be a good way to migrate the data from EMC --> HITACHI, then at a later date you can disconnect the EMC & get both FC working on the HITACHI.

Personally I would reccomend two FC to a hardware mirrored system, why are you mirroring, to protect yourself against failure, so why skip the FC card?

Tim