topic Re: Difference between LDEV and LUN in Operating System - HP-UX

Difference between LDEV and LUN

Srinikalyan — Wed, 13 Aug 2008 08:10:59 GMT

Hi,
Can someone explain the differences between LDEV(Logical device) and LUN(Logical Unit Number)? These names are confusing a lot.

Thanks,
Srinivasan

Re: Difference between LDEV and LUN

Duncan Edmonstone — Wed, 13 Aug 2008 08:24:55 GMT

Srinivasan,

If we're talking in the context of an XP disk array here, then the difference is pretty subtle, and you can pretty much use both terms as you like...

LDEV is a term to describe a piece of logical RAID storage carved out of the disks within an XP disk array. When an LDEV is presented out of a port on the XP disk array, the hosts see it as a LUN.

HTH

Duncan

Re: Difference between LDEV and LUN

Srinikalyan — Wed, 13 Aug 2008 08:54:11 GMT

Duncan,
Thanks. I got the differnce. One more query.
I have a Disk type of DKS2D-J300FC (300GB)
and Raid group of 3-1 which have 38 LDEVs.
What is that 3-1 means?

Thanks,
Srini

Re: Difference between LDEV and LUN

Duncan Edmonstone — Wed, 13 Aug 2008 09:29:08 GMT

Srinivasan,

Difficult to say

3-1 might be referring to the RAID level - in this case it means RAID 5 with 3 data and one parity blocks. The corect way to write this would be RAID 5 3D+1P, but this coukd shortened to 3-1

or 3-1 might just refer to the RAID group location within the XP

HTH

Duncan

Re: Difference between LDEV and LUN

Srinikalyan — Wed, 13 Aug 2008 09:58:30 GMT

Yes Duncan,

I think they are mentioning the RAID group location because the RAID level is RAID-5(14D+2P). Is that mean I have 16 number (14 for data and 2 for Parity)of 300GB disks?

Thanks,
Srinivasan

Re: Difference between LDEV and LUN

Duncan Edmonstone — Wed, 13 Aug 2008 10:09:37 GMT

Srinivasan,

Nearly - in actual fact for RAID 5 14D+2P what you actually have is LDEVs interleaved across 2 parity groups of 7D+1P

HTH

Duncan