LUNs and logical units!!

[wanhedagomes5887]

Can someone explain to me (like I'm five) what I LUN is and what a logical unit is? I've read explanations in the DCICN OCG (Official Cert Guide) book and resources on line, but it's just not clicking what these really are. It seems like a LUN can be a part of a drive or multiple drives, but not 100% sure. And I really don't have a good grasp of what a logical unit is (in respect to LUNs).

[mnaile]

When a RAID volume is created from multiple drives a LUN is created to allow access to the array. LUNs are simply the virtual drive id. 

Cheers,

Mark

[Brandon Rumer (Cisco)]

Exactly as Mark said, a LUN is basically a virtual disk. The LUN ID is just the identifier that you can then use to present it to a server.

In a SAN environment, you use RAID for disk parity (protecting against disk failure) and to create a big disk group. Its on top of this RAID disk group that you can create LUNs. You typically take those LUNs and present them via Fibre Channel or iSCSI to a server. That server thinks the LUN is a real locally-attached disk.