Facing errors while creating Multipath-Raid using mdadm

[Natasha3]

I have a server having two hdds (/dev/sdc and /dev/sdd) . Both hdds are same physical disk sent by two different paths to the sever (ISCSI Connection).  I am trying to create a multipath raid device using the following command :
"mdadm --create /dev/md0 --level=multipath --raid-devices=2 /dev/sdd /dev/sdc "
But facing error 
" mdadm: RUN_ARRAY failed: Invalid argument  "

my /etc/mdadm.conf  file
DEVICE /dev/sdd /dev/sdc
ARRAY /dev/md0 metadata=1.2 name=myarray:0 UUID=261fb9c:976d0d97:30bc63ce:85e76e91
Where UUID is some random generated unique UUID that I want to give to my newly formed md0.



Can anyone help me with this?

[techin]

Can you share more info about the product.. like what Server, model, storage info etc?

[Natasha3]

Hey , I am using INTEL S2600WFQ server board for making multipath . On this server I am getting 2 SAS disks (a same SAS physical disk via 2 different iscsi paths)  from 2 different servers which are connected to a same storage array. 

I am not very sure about the two servers and the storage array details as my work is only to create multipath on the INTEL sever.

disk:
NAME - HC530 
MODEL - WH721412AL5204

[utnoor]

Hi Natasha3,

May I know which OS you're using to create mdadm commands?

[Natasha3]

OS - Redhat 8.7 

[utnoor]

Hi Natasha3,

Kindly follow the example link from Red Hat itself on how to create software RAID.

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/managing_storage_devices/managing-raid_managing-storage-devices#creating-a-software-raid-on-an-installed-system_managing-raid

I hope that helps in resolving your issue

[utnoor]

Hi Natasha3,

We do not see option of multipath for mdadm as earlier found to be in RHEL 5/6.

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/5/html/installation_guide/s1-s390info-raid#s2-s390info-raid

[Natasha3]

Hey @utnoor , Thankyou for the reply .
I am asked to configure multipath only and not raid.

Is there any alternative for creating multipath instead of using mdadm?

or should one from the above discussion conclude that one cannot create multipath on 2 same disks (which host receives via 2 diffrent iscsi path) using any open source utilities on any open source OS present currently?

[utnoor]

Hi Natasha3,

When you try to create the software raid you get error " mdadm: RUN_ARRAY failed: Invalid argument " at the same time, when you check the log messages you should see error "md: personality for level -4 is not loaded!" which means the module for md_multipath is not loaded (i.e., for --level=multipath) & from developers we see is "MD_MULTIPATH provides a simple multi-path personality for use the MD framework. It is not under active development. New projects should consider using DM_MULTIPATH which has more features and more testing" ................And from the kernel source code it is available but **cannot** be loaded into the kernel..........like " dracut:Failed to install module md_multipath".....................for your scenario guidance follow this step by step guide.........https://www.qsan.com/data/dl_files/qs_wp_iSCSI-MPIO-in-Linux%20(en).pdf                                                                          ________________________xXx_____________________

[Natasha3]

Hey @utnoor ,
Followed the document "https://www.qsan.com/data/dl_files/qs_wp_iSCSI-MPIO-in-Linux%20(en).pdf" , multipath was created only on local disk and not the disks sent via ISCSI paths.

Can you help me with creation of multipath on iscsi disks? 

[utnoor]

Hi Natasha3,

Kindly follow the link & re-create the iSCSI LUNs as per the document however,

my suggestion would be to use multipath rather than madam (not as advanced as multipath)

[Natasha3]

 I tried re-creating LUNS as suggested by the document by making use of multipath instead of mdadm. But facing same errors. After receiving the ISCSI devices on my initator server , wwids/wwn of the devices changes making it difficult to make multipath on them.   

[utnoor]

Hi Natasha3,

If it works it can be used otherwise, it is better to use multipath rather than mdadm because , as we told earlier the module will not be loaded by default to support software RAID with multipath "MD_MULTIPATH provides a simple multi-path personality for use the MD framework. It is not under active development. New projects should consider using DM_MULTIPATH which has more features and more testing" 

To create the software RAID with multipath.........we require "md_multipath" module which is not available to load in RHEL 8.7 by default.......

The concerned information code is given in the below link............https://elixir.bootlin.com/linux/v3.8/source/drivers/md/multipath.c

[Natasha3]

Hey @utnoor ,
Tried all your suggestions.  Also used "DM_MULTIPATH" but I am unable to create multipath of my iscsi devices. 
The problem I am facing is that,
My iscsi devices (which is same physical devices sent via different paths to a server) are having different serial number, wwid, wwn number , iscsi id on the server when transferred to the server via two different controllers . 
Therefore whenever I try to make multipath them using "DM_MULTIPATH" i get error saying 
"only one orphaned path". It is not recognising other path (another iscsi device which is same physical device). 

[utnoor]

Hi Natasha3,

Please follow the link provided earlier to flush the multipath & re-create the maps to the LUNs

If any issues then it has to be checked at iSCSI end.

https://www.qsan.com/data/dl_files/qs_wp_iSCSI-MPIO-in-Linux%20(en).pdf    

[Natasha3]

@utnoor 

Hey Utnoor,

Checked this code.  
https://elixir.bootlin.com/linux/v3.19.8/source/drivers/md/multipath.c

Is this code under developement ? Is thiis code working? Can it solve our problems related to logical disks persisent naming of unique identifiers incase multipath?