vgcreate Large LUN

[joe_91]

I have two questions..

1. How do i vgcreate to accomodate a LUN which is 600G.

2. Also since the SAN has been connected how do i find the alternate PATHS to the disks since ioscan reports lot of disks. In other words how do i identify the same disk thru different controller PATHS?

THanks

Joe

[Torsten.]

I don't know what array you are using, but SAM will help you in both cases.

To advise about alternate pathes, some more information is needed.

[James R. Ferguson]

Hi Joe:

Look at the manpages for 'vgcreate(1M)'. You will see options to control 'pe_size', 'max_pe' and 'max_pv' in particular. You will need to assign appropriate values depending on the number of physical disk you have and their inherent sizes.

Depending upon the SAN to which you are connected, there may be utilities to easily identify alternate paths. EMC uses 'syminq'. Otherwise, you can 'pvcreate' all physical volumes and read the LVM header's PVID on each. Equality of the PVID values for two or more disks means that they are alternate devices of one another.

Regards!

...JRF...

[A. Clay Stephenson]

1) You need to set PS size to at least 16MB so that because the maximum possible number of PE's (64Ki) x PE size must be >= the largest PV.

2) The best way is to know you equipment well enough so that you don't have to ask. The second best way is to 1) vgcreate the VG using the one path that you do know. 2) Vgexport the VG using the "-s" option which will write the VGID into the mapfile 3) Create your /dev/vgxx direcory and /dev/vgxx/group device node and vgimport the VG using the -s option. In this case, vgimport will the system looking for the matching VGID supplied in the map file and will find the primary and alternate paths. If you have multiple PV's in this VG, you may wish to vgexport once again and vgimport using the (now) known paths to optimize the i/o paths because vgimport -s will probably not optimize the i/o.

[joe_91]

The SAN is EMC.

Thanks

Joe.

[joe_91]

After mkdir and mknod

vgcreate -s 128 -e 65535 /dev/vg01 /dev/dsk/cxtxdx (where the disk is 600 G).

will this work?

Thanks

Joe

[A. Clay Stephenson]

vgcreate -s 128 -e 65535 /dev/vg01 /dev/dsk/cxtxdx
Will this work?

Yes, except it's great overkill
(128 * 1024^2) * (64 ^ 1024) = 8TiB

The disadvantage to such a large PE is that you can lose a fairly big chunk if the disk size if not an exact multiple of PE size (ok so losing a little less than 128MiB on a LUN this big is no big deal) but I will still choose a PE size of 16MiB which will potentially waste less disk and still give you a maximum PV size of 1TiB.

[James R. Ferguson]

Hi Joe:

Well, yes:

128 * 1024 *1024 * 65635 ~ 8.7 TB

...even using the default value for 'max_Pv' which is 16 and which you didn't specify :-)) ...

...which is within legal limits defined in the tables for teh LVM chapter-16 of the HP Software Recovery Handbook):

http://www1.itrc.hp.com/service/iv/docDisplay.do?docId=prodITRC/DE_SW_UX_swrec_EN_01_E/LVM.pdf

Regared!

...JRF...