SAN topology will change, LUNs will change too?

[Wang Haitao]

Hi Guruz,

My SAN topology will be changed(include C7000 4Gb FC Pass-Thru modules will be replaced with 4/24 FC switch modules/Domain id will be change /fabric expanding etc.) The hosts that currently connect to the SAN are Windows 2003, RHEL 4.8, and VMware ESX 3.5. So my question is after finish these actions(replacement,changing domain id,expanding,etc), the hosts will recognize the corresponding LUNs normally(EVA4k, EVA4400 attached to the SAN)? or i need additional actions to do?

TIA

Jackie

[Wang Haitao]

Do i explain clearly? OK, i attach the topology fig. kindly see attachment. In C7000-1, there are 8 blades connect to SAN, 4 are VMware ESX 3.5, 4 are RHEL 4.8 64 bit. and 3 DL380 are windows 2003 (exchange cluster). before SAN topology changes, the eight blades connect to SAN by two 4Gb FC Pass-Thru modules(then connect to two 4/16 fc switches). now these pass-thru modules will replaced by two 4/24 fc switches. so after these things done and zoning finished correctly, the LUNs related to the corresponding hosts are present like before? or i need to do something? thanks.

Jackie

[Uwe Zessin · Accepted solution]

Hello Jackie,
a pure change to the Fibre Channel fabric will be transparent for Windows 2003 and VMware ESX V3.5 (as long as you don't change LUN addresses, but that is a storage array thing). I am fairly sure it is transparent for RHEL, too. It's been some time since I worked with Linux and SAN, but then there was no dependency on the N_Port ID (Fibre Channel address).

[Wang Haitao]

Hello Uwe,

Thanks for you reply. i'm glad to hear that. Fortunately, these OSes not like HP-UX which VGs need export/import even when the host attach to another N_Port. So these OS maybe use persistent hardware path(WWN?) like True64, right?

regards,

Jackie

[Uwe Zessin]

Ha! ;-)

Tru 64 Unix does _not_ use a persistent hardware path. It uses persistent binding based on the LUN WWN. That's why you can even move an EVA's virtual disk to a different LUN address.

VMware ESX V3 and up use that LUN WWN, too, but use additional information to be able to detect volume clones. Windows uses the disk signature and RHEL offeres different methods (it depends on whether you use the file system directly or go through a volume manager).

[Wang Haitao]

Wow, thank you very much, i learned a lot! :)
the RHEL using whole disk as a file system approach, eg. sda mount on /ora1 sdb mount on /ora2 and so on.

[Uwe Zessin]

OK. That is pretty transparent as long as you don't have multiple arrays and make topology changes.

Still that can be worked around if you give the file system a label and use it in /etc/fstab or use put the file systems UUID into fstab.

[Wang Haitao]

hi,
thank you very much. uuid sounds wonderful.:)