Alternate disk in vgcreate

[ShivKumar_1]

Hi,
When I m trying to extend a volume group, the disk which I add , goes always as a ALTERNATE link is there a way I can avoid that.
I have two LUNS of 83GB each, I want to get 166GB on my volume grp but it comes up only as 83GB. I tried difft ways but not succesful any ideas?

I DONT WANT THE 2ND DISK TO BE ALTERNATE LINK

Thnks

[Kent Ostby · Accepted solution]

Shiv --

You need to double check the device file that you are specifying.

LVM will only make something an alternate link if that is what it really is.

In other words, you need to be sure that the device file you are specifying is for a second unique disk drive.

Best regards,

Kent M. Ostby

[Sudhakar.J]

Hi,
If both device files points to the same disk then LVM will take the second device file as alternate path only.
If it is so then u cannot add the second device as additional disk.
You can check up whether both links(device files) points to same disk or not thru lssf command.

ATB,
Sudhakar

[RolandH]

Hi Shiv,

this is because you have TWO scsi/fc connections to one array, which are using the same internal bus of your attached array. So the disk is detected two times from the system over two differant hw pathes. So you have ONE disk with TWO device files for that disk. The LVM detect this special configuration and use the "second device" for the alternate link. What means if the first scsi/fc connection is brocken the LVM switches two the second path and your disk is further available.

Do you know how many physical disk you system has?

do an "ioscan -fnCdisk" and count the disks (CDROM will also count as disk). Are there more than you expected !!!???


HTH
Roland

[Todd McDaniel_1]

Shiv,

A way to tell for sure is to use the inq or syminq if you have that installed for EMC. If you are using EMC if not then HP or compaq should have similar commands to see if it is an alternate disk path and not really a second disk.

If you are using EMC run the inq -sortsymm command and capture it in a file.

Look at the disk devices that you are referencing here... If they have the same Serial number then teh are in fact the same disk....You merely have dual pathing to the SAME DISK...

[Sunil Sharma_1]

Hi,

can you post the o/p of ioscan -funC disk ?
i think you have only one lun with two Path that's why you are able to add only one Lun and other is coming as alternate path.

Sunil

[Tim Adamson_1]

You don't have any choice. Effectively you have one LUN/DISK but two paths to that LUN.

Consider the analogy of a door. You have one door, but two ways of getting to the door - from the inside and the outside. A pretty crap analogy I must admit.

So in your case you only have 83Gb of disk space and NOT 166Gb.


Tim

[ShivKumar_1]

Hi Experts,
The issue is resolved as pointed out by others the two LUNS point to the same physical disk. So as in this case, whenever you add the 2nd LUN it takes it as a alternate path.

Pl close this thread
Thnks
SK