topic Re: path the same? in Operating System - HP-UX

path the same?

Francis Flan — Wed, 31 Oct 2007 05:29:16 GMT

Hi,

When disks on an EVA4k are presented to 2 servers in different locations, will the ctd paths or HW paths be the same.

I need to know which paths are pointing to the same disk on the EVA.

Re: path the same?

Mike Shilladay — Wed, 31 Oct 2007 05:44:29 GMT

Hi Francis,

That depends on the interface that is used for the presentations. It would be unwise to assume that they would be the same until it was proven. In theory they should if you use the same bus.

I have had two identical servers, but the disks were all one number higher on the cX part of the path. An HP engineer stated that it depends on which bus the kernel finds first.

Mike.

Re: path the same?

Francis Flan — Wed, 31 Oct 2007 06:04:56 GMT

Thanks for your reply Mike.
Heres the output of ioscans on both machines if it helps.

Ive no idea which is which. Some disks are different sizes though.

Re: path the same?

Duncan Edmonstone — Wed, 31 Oct 2007 06:43:11 GMT

Francis,

They can be the same, but more often than not they aren't!

The way to figure this out is to look at the part of the HW path thats for the Storage rather than for the HBA. So in your case it looks like both hosts have a FC HBA at path 0/3/0/0/0 - the rest of the HW paths are the storage. So very quickly looking at your EVA, we can see 4 virtual buses (the cX in cXtYdZ), which appear to match up as follows:

Server A Server B
c1 c2
c4 c1
c6 c5
c3 c7

The tYdZ part of the device file is usually consistent.

For further checking download the relevant version of evainfo from here and look at the WWIDs of the disks on each host.

http://h20000.www2.hp.com/bizsupport/TechSupport/DriverDownload.jsp?prodNameId=3439051〈=en&cc=us&prodTypeId=12169&prodSeriesId=471497&taskId=135

HTH

Duncan

Re: path the same?

Mike Shilladay — Wed, 31 Oct 2007 06:47:00 GMT

Hi Francis,

The ioscan proves that the two disk presentations are different. What gives the game away is the OS disk with the suffix s1, s2, s3 - no two OS disks have the same address.

My suggestion would be to see if the disks are different sizes, then you could identify which disk was which. Use the diskinfo command on the raw device.

e.g. diskinfo /dev/dsk/c7t0d1

Look for the size in KB and try and match on the other server. If you add additional disk later it maybe useful to do one disk at a time, i.e. create disk, present to server A, present to server B, create next disk, present to server A, present to server B so on and so forth. Tedious I know.

Mike.

Mike.

Re: path the same?

Francis Flan — Wed, 31 Oct 2007 09:53:25 GMT

thanks for the help guys
Im at the final hurdle. There are 2x100GB LUNs. Can you match them based on this info?

Server 1:
c7t0d4 100GB 0/3/0/0/0/0.20.0.35.0.0.4
c5t0d4 100GB 0/3/0/0/0/0.20.0.17.0.0.4
c1t0d3 100GB 0/3/0/0/0/0.10.0.33.0.0.3

Server 2:
c1t0d3 100GB 0/3/0/0/0/0.10.0.32.0.0.3
c4t0d3 100GB 0/3/0/0/0/0.10.0.33.0.0.3
c6t0d4 100GB 0/3/0/0/0/0.20.0.17.0.0.4
c3t0d4 100GB 0/3/0/0/0/0.20.0.35.0.0.4

Also why can I only see 3 path on the first server? Might this be a problem with secure path or a zoning issue?

Re: path the same?

Mike Shilladay — Wed, 31 Oct 2007 11:38:19 GMT

Hi Francis,

By my reckoning based on the info you have provided. (by the way, have you changed server a and b around since your attachment? Also do you have alternate paths?)

Anyway, I would suggest that
Server 2:
c7t0d4 100GB 0/3/0/0/0/0.20.0.35.0.0.4 =
c5t0d4 100GB 0/3/0/0/0/0.20.0.17.0.0.4 +
c1t0d3 100GB 0/3/0/0/0/0.10.0.33.0.0.3 @

Server 1:
c1t0d3 100GB 0/3/0/0/0/0.10.0.32.0.0.3
c4t0d3 100GB 0/3/0/0/0/0.10.0.33.0.0.3 @
c6t0d4 100GB 0/3/0/0/0/0.20.0.17.0.0.4 +
c3t0d4 100GB 0/3/0/0/0/0.20.0.35.0.0.4 =

Match the symbols (@, +, =) at the end of the line, to get the corresponding LUN's. Notice I have also changed the servers around to reflect the first attachment.

As to trying to explain why you cannot see path c2tXdY on server 2 (as stated by above) is that
a) you may need to do another ioscan on server 2, followed by insf -e, or

b) It maybe the secure path, as you can specify and restrict (as i understand) the host access.

Mike.

Re: path the same?

Francis Flan — Wed, 31 Oct 2007 16:19:25 GMT

thanks for all your help today with special mention to Mike

Re: path the same?

Mike Shilladay — Thu, 01 Nov 2007 04:26:20 GMT

Hi Francis,

You are most welcome. Glad to be of assistance.

Mike.