Lun Offset concept ?

Hi,

Use extreme caution when enabling lunoffset.  Improper use of this command can cause the host to lose access to its devices.

It is recommended that the affected host be offline for this procedure.

The format of this command is:

symmask -sid -wwn set lunoffset on -dir <#> -p <#>

Windows only supports LUNs in the range 0-254.  If it is necessary to assign LUN numbers higher than this to a server, lunoffset can be used to make the LUN number that is presented to the host lower than the actual LUN number.

To do this, determine the lowest LUN number assigned to the host and use lunoffset with a base value of 0 and the offset equal to the lowest LUN number.  The offset will be subtracted from all the LUN numbers so that the lowest LUN will be presented to the host as LUN 0.

For example, if the host had LUN numbers 0x100 and 0x101 assigned to it, you would use the following command which would cause the host to see them as LUNs 0 & 1:

good paper that explains the concept

Symmetrix Dynamic LUN Addressing Technical Note

lunoffset functionality has been superseded by dynamic lun addressing. This functionality on the array dynamically allocates LUN address based on host presentation and not FA address. So you could have a device mapped to FA address 101 (hex)  which is 257 decimal ..many OSs would not be able to see that LUN, but if you were using dynamic lun masking and this was only the second device being masking to this host, it would show up on the host at LUN address 2, even though it's still mapped to FA at address 101. Vmax uses dynamic lun addressing out of the box where on DMX3/4 you have to append -dynamic_lun option whenever you are masking devices.

Good boy... good boy. You learned it the hard way, isn't it? ;-)

Hi

I have lun offset up the following way on a dmx and i will have to do the same on the vmax as part of a migration. But, since lun offset has been superseded by dynamic lun addressing, is there a way to achieve this exactly using dynamic lun addressing?

Primary volumes 000-200

Clones volumes 201-400

When primary volumes needs to be scan by the host,Set the offset as

symmask -sid xxx lunoffset on 400 201 -dir

Right, but i cannot manipulate if the host has access to the primary volumes or clone volumes, by using the lun offset?.

It can be done by creating different storage groups and modifying it as needed. I was just wondering if that is the best way to do it.

Rj,

You can specify a starting LUN address when adding devices to a storage group that is already part of a masking view... just add a -lun flag onto the end of your symmaccess command, e.g.:

symaccess -sid 1234 -name SG1 -type storage add devs 1F0:1F1 -lun 200

Thanks,

- Sean

Correct, you would have to take the devices out of the Storage Group and then add them back with user-specific LUN IDs.

Right..i was just curious to learn if there is a different way.

Thanks

Rj