Device name assignment for shared disks

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Hi,

I'm testing an option to deploy Oracle RAC on RHEL 6.4 guests in 3.2 and enabled few shared disk between 2 guests - 2 Gb , 10 Gb and 50 Gb.

After reboot all disk are recognized in OS but on each guest they appear as different devices . It means that on VM1 2Gb disk was recognized as /dev/vdb in VM2 it visible as /dev/vdc , 10Gb as /dev/vdc and /dev/vdb respectively .I expect they all shared disk will have the same names .

Is there way to manage this issue ?

Regards ,

Vladimir Berezovski.

nd
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Responses

BH Active Contributor Newbie 284 points
20 June 2013 2:42 PM

If you use LVM you can give each volume group a name, and then it doesn't matter so much how the disks get assigned because you're not using that anyway.  E.g. I have seen some people name it after the server .

With a server name of alpha, the VG would be /dev/alpha, and the rootfs LV would be /dev/alpha/rootfs .  I think this was a way to prevent conflicts where many VGs are named VolGroup00 thus the O/S gets confused (I think).

But for your situation, you probably want to name the disks some other way.

Sadique Puthen's picture Red Hat Guru 4649 points
20 June 2013 3:56 PM

You can use udev rules inside the guest to map the disks using it serial number to specific device names.

RJ Red Hat Active Contributor 337 points
20 June 2013 6:30 PM

Couple of possible solutions I can see:

  1. If the disks have a serial number assigned to them (not sure if that's possible in RHEV-M, but it's certainly possible in libvirt/qemu) then you should be able to refer to the disks by a path such as /dev/disk/by-id/...
  2. Assign known UUIDs or LABELs to the filesystems in the disks.  That'll let you mount them using a UUID, the device name won't matter.
nd Pro 500 points
22 June 2013 12:38 PM

 

At present neither fs was defined on shared disks .

I tend  to configure the udev rules for the /dev/vdX  devices but I cannot reveal their UUID   to edit /etc/udev/rules.d/ file and assign a names for my  devices   . But  the following command  didn't give any output 

#scsi_id --device=/dev/vdb  

The same result  with :# /sbin/scsi_id -g -u -d /dev/vdb

I wanted to enable UUID  by editing the  /etc/scsi_id.config   but doesn't exist although  should be :

# rpm -qc udev-147-2.46.el6.x86_64
/etc/scsi_id.config
/etc/sysconfig/udev
/etc/udev/udev.conf

# ll /etc/scsi_id.config
ls: cannot access /etc/scsi_id.config: No such file or directory.

Create a new one ? Is there its  example for  RH6 ?

I ran  "udevadm test /block/vdc"  - it  has a lot of output   but I found this line:

node_symlink: preserve already existing symlink '/dev/disk/by-id/virtio-63a5887e-5b49-4f87-b' to '../../vdb'

Is the virtio-6cc66b28-c7c0-4def-8  may be used in the udev rules  as UUID  ( UUID is 63a5887e-5b49-4f87-b ) ?

/Vlad.

 

 

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