As a follow-up to my previous post about MPIO software and RDMs, I suggested SDDDSM could help you map Windows volumes to Storwize volumes. This led to the obvious question: What about Linux VMs?
In a distant time there was a version of IBM SDD for Linux (in fact you can still download it). But because it was closed source and used compiled binaries, it meant that users could only use specific Linux distributions/Kernel versions. This was rather painful (especially if you upgraded your Linux version due to some other bug and then found SDD no longer worked). Fortunately native Multipathing for Linux rapidly matured and offered a simple and native option that is definitely the way to go (and please don’t listen to the vendors pushing proprietary MPIO software, integration native to the Operating System using vendor plug-ins is in my opinion the only acceptable MPIO solution).
Either way, it turns out you don’t even need multi path software to map a Storwize Volume to an Operating System device.
In this example I have created a volume on a Storwize V3700 with a UID then ends in 0043.
It is mapped as a pRDM to a VM, I can see the same UID under the Manage Paths window. You can see the same UID at the top of the window (ending with 0043).
On the Linux VM that is using this VM, I want to confirm if the device /dev/sdb matches the pRDM. In this example we use the smartctl command. We can clearly see the matching Logical Unit ID (ending in 0043), so we know that /dev/sdb is indeed our pRDM.
[root@demo-oracle-4 ~]# smartctl -a /dev/sdb smartctl 5.43 2012-06-30 r3573 [x86_64-linux-2.6.32-573.3.1.el6.x86_64] (local build) Copyright (C) 2002-12 by Bruce Allen, http://smartmontools.sourceforge.net Vendor: IBM Product: 2145 Revision: 0000 User Capacity: 5,368,709,120 bytes [5.36 GB] Logical block size: 512 bytes Logical Unit id: 0x60050763008083020000000000000043 Serial number: 00c02020c080XX00 Device type: disk Transport protocol: Fibre channel (FCP-2) Local Time is: Sat Apr 16 23:16:09 2016 EDT Device does not support SMART Error Counter logging not supported Device does not support Self Test logging [root@demo-oracle-4 ~]#
If you find smartctl is not installed, then install the smartmontools package:
yum install smartmontools
If we have Linux multipath configured, we can also use the multi path -l (or -ll) command to find the UID and determine which Storwize Volume is which Linux device. Again I can easily spot that mpathb (sdb) is my Storwize volume with the UID ending in 0043.
[root@centos65 ~]# multipath -ll mpathb(360050763008083020000000000000043) dm-6 IBM,2145 size=5G features='1 queue_if_no_path' hwhandler='0' wp=rw `-+- policy='round-robin 0' prio=50 status=active `- 5:0:1:0 sdb 8:96 active ready running
So Linux users will actually find it quite easy to map OS disks back to the Storwize volume.