LUN numbers presented to a host

[Rahul Khare]

Dear all,

I have a question, we are having HP storage in our datacenter which is currently having 17 (9old+8new) LUNs presented to one of the host.

This host was a dev/qa oracle box earlier and has recently been bifurcated to contain only the dev database. We added 8 new LUNs (which autmatically got the LUN numbers 10,11,12....) on this host and did not destroy the older 9 LUNs (LUN numbers 1,2,3,4...).

My question is, in case I decide to use the older 9 LUNs (Vdisks) by unpresenting it from the host, would I face any problem of the newer LUNs getting the numbers starting from 1-9? Since the host currently uses
/dev/sdj, /dev/sdk....so on, the change in the LUN number would make it /dev/sda, /dev/sdb... and so on.

In theory, I know that the LUN numbers would not change but has someone tried it practically?

Thanks & Regards,
Rahul Khare.

[Hasan Atasoy]

hi raul;

if you unpresent first 9 lun, the new 8 lundevice adrdres will be renumbered like /dev/sda /dev/sdb . if you are mounting filesystems directly in fstab like /dev/sda /u1 ... you will get trouble.

but if you are mounting filesystems by label . no problem will occur.

touch a file under each mount point like ( assume that you have /u01 /u02 ... ) /u01/sdadisk /u02/sdbdisk according to disk names..
put # on each mount point in fstab .
reboot server and correct fstab according to new disk names...

Hasan.

[Vasiliy Karpov]

On HP-UX host device names will not change in case you unpresent LUNs. Device files for unpresented LUNs will be in NO_HW state untill reboot. After reboot they will disappear. Generally it depends on operating system how device files behave.

[Ivan Ferreira]

Considering the device names that you are talking about, it seems that you are talking about Linux.

Linux will change the device names and order on reboot. What you can do is to configure uudev to create persistent device names. For information about persistent device names see:

http://www.redhat.com/docs/manuals/enterprise/RHEL-5-manual/Virtualization-en-US/ch-virt-lun-persistence.html