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AIX LUN major minor vs serial#

Posted on 2014-02-07
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Last Modified: 2014-02-14
we have a RAC system with LUNS attacjed to both nodes we have created ASM aliases using major and mainor number..

ASM1 till ASM 10 are correctly showing the major minor numbers in both nodes...
and everything is running fine..
and this is best practice by IBM and ORACLE.

but we have a new Jr SA who is saying this is wrong as although major and minor are the same for each LUN on both Nodes the Lun Serila number is different.

we know that the configuartion is correct.
but how LUN serial could be different and major minor are identical?
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Question by:it-rex
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by:David
David earned 400 total points
ID: 39843022
Well, I write a lot of low-end SCSI code so will answer from the engineering perspective. I have no idea what the architecture of the hardware you have, so this is more of a generic answer.

1. The serial number of any SCSI device must be unique for compliance (of this type hardware).  It does not matter what device driver you use, or path, or anything else.  You send a command to read the SCSI EVPD page, and you must get the unique identifier for the hardware.

2. In a RAID configuration or any virtualized environment, the controller has an obligation to create a unique identifier for every unique LUN.  Not everything plays nice, and the revision of the SCSI spec that a RAID system is compliant to won't necessarily present a unique serial number.

3. The above serial numbers are the SCSI device unique identifiers. There are also WWN port and node identifiers which are not technically serial numbers, but must be unique or you break a fabric, but still it could work on certain hardware.

I expect you are confusing the SCSI device serial number with the WWN port/node addresses which are not serial numbers.

In order to answer your question on what is right, you need to be more descriptive and report exactly what you have and how you obtained it.
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by:it-rex
ID: 39843119
Although 2 disks on 2 nodes are using the same major and minor number

Will it be possible that output of lscfg will show 2 different serial numbers.
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woolmilkporc earned 1600 total points
ID: 39843434
The string shown by lscfg contains the machine model/serial (the first 3 blocks) and the hardware location code of the HBA serving the disk (the three character  pairs following the first hyphen, separated by hyphens). Then follow WWN and LUN.

On different machines it may well be expected (yet not necessarily) that the hardware locations of the HBAs are also different. In any case the machine serial will be different.

The WWN and the LUN should be the same, however.

The whole string is composed of

machine model . nnn . machine serial - HBA location - WWN of the storage device - LUN number

The PVID of a disk is always the same across machines (check with lspv).

You can also run

lsattr -El hdiskxxx

and you will see several more identifiers (e.g. FC Node Name, Device Unique Identification etc.)
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by:it-rex
ID: 39843579
So what would explain having 2 LUNS shared between 2 lpars
With same major and minor
But lscfg shows different lun names
??????
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by:it-rex
ID: 39843668
both
hdisk8@node1
and
hdisk4@node2

they have the major and minor numbers

ls -la hdisk8
brw-rw----    1 grid     asmadmin     18, 14 Jan 17 09:02 hdisk8

ls -la hdisk4
brw-rw----    1 grid     asmadmin     18, 14 Jan 17 09:11 hdisk4


@node1

lscfg -vpl hdisk8
  hdisk8           U9179.MHD.10854A0-V42-C42-T1-W500507680140B9D7-L32000000000000  MPIO FC 2145

        Manufacturer................IBM    
        Machine Type and Model......2145            
        ROS Level and ID............0000
        Device Specific.(Z0)........0000063268181002
        Device Specific.(Z1)........020060c
        Serial Number...............60050768018305CFC000000000000B8C


@node2

lscfg -vpl hdisk4
  hdisk4           U9179.MHD.10854A0-V44-C44-T1-W500507680140B9D7-L22000000000000  MPIO FC 2145

        Manufacturer................IBM    
        Machine Type and Model......2145            
        ROS Level and ID............0000
        Device Specific.(Z0)........0000063268181002
        Device Specific.(Z1)........020060c
        Serial Number...............60050768018305CFC000000000000B7C

As you have mentioned the I think I see both
The WWN and the LUN are the same.
but what is the line that says

Serial Number means and what it signifies?
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Expert Comment

by:woolmilkporc
ID: 39843943
It seems that these nodes are running as LPARS with dedicated HBAs (or NPIV) on the same hardware (Power 780).

Anyway, the LUN number is not the same! hdisk8 has LUN 32 and hdisk4 has LUN 22.

The serial number is composed of parts of the WWN and some more information. This number is unique, and is also different, as you said.

So I'm rather sure that these are different disks!

The major/minor numbers aren't of any significance across nodes, they're only used internally. Up to now I wasn't aware that you could create an ASM diskgroup using major/minor! Or do you mean the "/dev/hdiskx" entry instead?

There is a really unique disk identifier at a higher level in AIX, which is the PVID. This identifier is written on the disk and cannot change.

Run

lspv

on the nodes and search for hdisk4 and hdisk8, respectively. If the displayed IDs (second column) are different you can be really sure that these disks are not the same!
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by:it-rex
ID: 39844299
With ASM on AIX we can not have PVID it is a requirement for pvid to be null
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by:woolmilkporc
ID: 39844311
OK,

but the disks come from the same storage server (SVC) and have different LUNs, so they are different disks.

Moreover, thay have different serial numbers.

You can check these numbers on the SVC by means of the "lshostvdiskmap" command.

Here, too, you will see that it's two different disks.
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Author Closing Comment

by:it-rex
ID: 39860311
thanks all
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