Understanding LUN

an example would be better.

let's say I have 16 disk array block.
on the disk array utility, I configure :
 
Disk 1 to disk 3 as RAID5
Disk 4 to disk 6 as RAID5
Disk 7 to Disk 10 as RAID5
Disk 11 to diak 16 as RAID 0

In the disk management utility:

I will format and name :

Disk 1 to disk 3 as RAID5 as disk G
Disk 4 to disk 6 as RAID5 as disk H
Disk 7 to Disk 10 as RAID5 as disk I
Disk 11 to diak 16 as RAID 0 as disk K


now what's the point of creating LUNs ???

thanks

My answer from your original question:

Do you know what a LUN is?

     http://en.wikipedia.org/wiki/LUN
     http://www.webopedia.com/TERM/L/LUN.html

You need to define a LUN so that when the I/O command is sent down the bus the drives know which ones (either real or virtual) the I/O command is to.

It sort of like putting a person's name on the outside of a envelope when you send them a letter.    If there are 8 people living in a house, they all  have the same address ("bus").  So you need to put their name ("LUN") on the outside of the envelope also so they know exactly who in the house the letter is for.

Better yet, it is like a TCP/UDP port on a sever.  You don't send a packet just to an IP address, you send it to a port and address.


To expand based on your arrary example.  Windows knows about the "G", "H", "I", and "K" drives.  The RAID arrary  and the SCSI controller don't.  They know about LUN's.  The G drive may map to LUN 01 and the H to 02 and so on.  When the I/O is issued at the SCSI level, it is issued to LUN 01, not to "G" drive.  

If I understand well LUNs refer to individual SCSI disks.

OK

G,H,I,K disks are setup through disk management in windows
RAID5 and RAID0 are set up through Disk Arrray Utility(SmartStart disk)
What about LUNs which utility is used to set up LUNS?

No, LUN reference the logical units, not the physical units.

A single LUN could referer to all 16 physical devices on a a single SCSI controller.  The host sees a LUN as a single logical drive.

This may help some more www.storageheaven.com/downloads/raid-techsummary.pdf

if you look at the SAN storage management through w2003 server R2 ,
There are subsystems, I guess this refers to each block of SCSI disks that are connected to each Host adapter. By the way I don't know how many host adpaters we need for 16 SCSI disks.

when you create a LUN in a certain subsystem you gave it a name and size and then you can assign a drive letter to the same LUN and format it and assign volume name.

seeing all these  actions, does it mean that you don't need to do anything from the Windows Disk Management console?

because Assigning drive letters and formating used to be done through Disk Management.

and if you extend the LUN, would the volume assigned to the LUN get extended automatically?

--> and if you extend the LUN, would the volume assigned to the LUN get extended automatically?

I would not get extended automatically.  You MIGHT be able to extend it manually.   Umm, this I would have to read up, I have never tried, nor have I thought about doing it.  My initial thought is that you would need some special utility, like Partition Magic, as you are changing the size of a "partition."

I know that under Linux/Unix you can have logically volumes that are mapped to one or more paritions.  You could map a logical volume to one or more LUN's.  Then you could create a new LUN, add that to the logical volume and increase the size of a logically volume.  I am not 100% sure, but I think that Windows supports logical volumes and so you should be ablt to do the same thing.

thank you all for your help

I may come back later for another question in the same topic LUN