Static versus dynamic domain ids

[stephen2615]

Hi All,

Is there any benefit to using static domain ids over letting the switch assign them?

Stephen

[inch]

Hi,

it doesnt _really_ matter but by providing static domain id's it makes it easier to swap out a core switch on the fly :-)

Of course, I'm pretty sure it would be pretty rare that you would need to do this :)

Cheers

Andrew

[stephen2615]

Hi Andrew,

Lets hopes I don't do that often. I suppose static domain id's need to be managed externally and that is just a waste of good drinking time..

Stephen

[tblancha]

Drinking time is important and shouldn't be missed. But static ID's are neccessary in some situations. For instance, there are particular ranges of domain ID's that need to be used in particular interop modes. Or what if you wanted to move to a MDS and have the same domain ID's as what was in place before. In IVR1, it is terribly important to have unique DID and so the config guide suggests to verify uniqueness and then set DID to static. I like to use it as an admin guide-I make first switch 1 and 2nd switch to be 0x2, etc and this tells me who is attached where.

[stephen2615]

I did note that Domain IDs are restricted to the 97 to 127 range when using inter op and that HP (perhaps HP-UX) and IBM (AIX) don't like to find the Domain ID has changed. I don't have any plans in the future to use interop modes as I told the users, I will only support Cisco from now on. HP wanted to use Brocade for their gear but they gave in. We are using a lot of HP blades that will have to be attached to the SAN but I don't know if Linux has the same issue at HP-UX when it comes to Domain IDs.

I did like the idea of knowing which switch the system is connected to by looking at the Domain ID and to be honest larger hex numbers take a minute to digest.

Stephen

[huangdc]

I strongly suggest to use static domain ID. It will not only simplify management but also make SAN more stable.

[stephen2615]

Hi,

It sounds like the course of action is to use Static Domain ID's. Especially as I am configuring the switches and will be attaching huge amounts of storage in a day or so.

Thanks for your reply.

Stephen

[DavidSAnderson10]

Use static domains and persistent fcid's. Bad things happen to HP-UX devices (and some AIX versions) when the domain id changes. Windows, OpenVMS etc dont care. They track the WWWN of the LUN not the domain and port of the switch connection.

[tblancha]

Technically, it's the FCID of the target not the server that needs to stay the same for AIX and HPUX. So, as long as the storage gets the same FCID then you are good for those OS's. Linux does not have this issue but likes/prefers to have persistent LUN's allocated to it in the HBA or OS but is not required. In general, it considered good practice to let the domain come up and get assigned a DID from the principal switch. If that DID is acceptable to you as the admin, then simply make it static.

[a-watkins]

...it makes it a lot easier to read the fcns database if the domain IDs are static (you know where you are rather than needing to refer back to the domain ID allocations to work out which DID is which switch).

The HPUX and AIX issue (although I believe AIX 5.2/5.3 has a solution for this) means that device files in the OS are generated based upon FCIDs, so if the domain ID of the storage port changes, the FCID of the storage port changes so the device file no longer refers to the LUN you are looking at. You then need to do some Volume Manager reconfiguration to tell the host where its storage has gone.