Difference between LDEV and LUN

[Srinikalyan]

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

Thanks,
Srinivasan

[Duncan Edmonstone · Accepted solution]

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

[Srinikalyan]

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

[Duncan Edmonstone]

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

[Srinikalyan]

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

[Duncan Edmonstone]

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