Persistent ISCSI disks name

Last few days I was working on Oracle cloning possibility using storage snapshots (post will be blogged soon) and I hit a ISCSI issue at the very beginning.
I have been playing with restarting storage and Linux box and from time to time ISCSI disk has been mapped to different block devices (/dev/sdb1 instead of /dev/sdc1). I really need to keep this persistent and I found this instruction for RedHat Linux (so it should work for OEL and CentOS).

Additionally I was looking for possibility to check how IQN shared on storage is mapped to Linux block devices. There is a nice directory layout where you can check that.

[root@piorovm by-path]# pwd
/dev/disk/by-path
[root@piorovm by-path]# ls -l
total 0
lrwxrwxrwx 1 root root  9 May 11 13:01 ip-10.10.20.241:3260-iscsi-iqn.1986-03.com.sun:02:6fe1e73d-8d7a-6ee7-8446-db844ae0d0c7-lun-0 -> ../../sdc
lrwxrwxrwx 1 root root 10 May 11 13:01 ip-10.10.20.241:3260-iscsi-iqn.1986-03.com.sun:02:6fe1e73d-8d7a-6ee7-8446-db844ae0d0c7-lun-0-part1 -> ../../sdc1
lrwxrwxrwx 1 root root  9 May 11 13:01 ip-10.10.20.241:3260-iscsi-iqn.1986-03.com.sun:02:f6746dbb-c95f-e2dc-8bb6-c82d3ef5169a-lun-0 -> ../../sdb
lrwxrwxrwx 1 root root 10 May 11 13:01 ip-10.10.20.241:3260-iscsi-iqn.1986-03.com.sun:02:f6746dbb-c95f-e2dc-8bb6-c82d3ef5169a-lun-0-part1 -> ../../sdb1
lrwxrwxrwx 1 root root  9 May 11 13:00 pci-0000:00:07.1-ide-0:0 -> ../../hda
lrwxrwxrwx 1 root root 10 May 11 13:00 pci-0000:00:07.1-ide-0:0-part1 -> ../../hda1
lrwxrwxrwx 1 root root 10 May 11 13:00 pci-0000:00:07.1-ide-0:0-part2 -> ../../hda2
lrwxrwxrwx 1 root root  9 May 11 13:00 pci-0000:00:07.1-ide-1:0 -> ../../hdc
lrwxrwxrwx 1 root root  9 May 11 13:00 pci-0000:00:10.0-scsi-0:0:0:0 -> ../../sda
lrwxrwxrwx 1 root root 10 May 11 13:00 pci-0000:00:10.0-scsi-0:0:0:0-part1 -> ../../sda1
[root@piorovm by-path]#

When you know which IQN is pointed to which block devices we can use mentioned RedHat instruction with some additional remarks.

Here is output from my configuration

1. Check WWID for block devices

[root@piorovm ~]# scsi_id -g -s /block/sdb
3600144f04be80ec000000c2936224200
[root@piorovm ~]# scsi_id -g -s /block/sdc
3600144f04be7ffdf00000c2936224200

2. Go to
   

   [root@piorovm ~]# cd /etc/udev/rules.d/
   

   and create a file called 20-names.rules Replace my WWID with results from scsi_id command and put correct names

   [root@piorovm rules.d]# cat 20-name.rules
   KERNEL=="sd*", BUS=="scsi", PROGRAM="/sbin/scsi_id -g -s", RESULT=="3600144f04be7ffdf00000c2936224200", NAME="sdc"
   KERNEL=="sd*", BUS=="scsi", PROGRAM="/sbin/scsi_id -g -s", RESULT=="3600144f04be80ec000000c2936224200", NAME="sdb"
   

   Here is a change with RedHat doc – use double equal mark "==" instead of one equal mark "=" for compare (KERNEL, BUS,RESULT).
   
   
3. Save file and start
   

   [root@piorovm ~]# start_udev
   Starting udev:                                             [  OK  ]
   [root@piorovm ~]#
   

regards,
Marcin