LUN Clear Host residuals in Red Hat linux

[vijay alur alur]

Hello All,

I have a Red hat linux server running 6.3 version OS. And below is the problem description.

I assign a LUN to the server today with LUN ID as 4 from SAN. I scan that LUN and use it for my applications using LVM. i use that LUN for couple of months. After few days i do not need that LUN anymore, so i remove that LUN from LVM and release it to the storage pool.

After few days, there is one more requirement for LUN, and i assign the same LUN with LUN ID 4 to the server again. And it still hold the old information from the last time it was assigned to the server.

How can i clear the Old LUN information from the server before assigning the same LUN again to the server?

In HPUX there is a command scsimgr replace_wwid option to achieve this.

Thanks,

VJ

[Matti_Kurkela · Accepted solution]

This is related to Linux hot-plugging: once the kernel has seen a particular device, it tries to make sure that the device can keep the same device name(s) whenever possible, even after it is temporarily disconnected. To make the kernel completely forget a particular device, you will need to tell it that the removal is intentional.

The full RedHat-recommended procedure can be found in the RHEL 6 Storage Administration Guide:

https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/removing_devices.html

In a nutshell:

• unmount filesystems, reduce disk out of LVM and/or otherwise stop applications from using it
• if you use dm-multipath, identify the individual /dev/sd* devices with "multipath -l", then remove the multipath device with "multipath -f <multipathname>"
• run "blockdev --flushbufs /dev/sdX" for the devices that will be removed (= component paths of the multipath device that was removed in the previous step). This ensures that all forms of disk I/O have been completed for the device(s).
• finally tell the kernel to forget the /dev/sdX device(s): 

echo 1 > /sys/block/sdX/device/delete

If the LUN was already unmounted, removed from the LVM and un-presented, you'll only need the "multipath -f" and "echo 1 > /sys/block/sdX/device/delete" steps. The "blockdev --flushbufs" step won't do any good if the disk/LUN is no longer accessible.

You may also want to remove the WWID of the LUN from /etc/multipath.conf, if you used a custom multipath alias for the device, or from /etc/multipath/bindings, if you used the user_friendly_names feature of dm-multipath.

[vijay alur alur]

Hi Matti,

Thanks for the reply!

I will try these steps.

Regards,

VJ

[vijay alur alur]

Accepted your post as  a solution to my problem, a well deserved kudos given!!!

Thankyou!!

VJ