max luns/hba (502 Views)
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Frequent Advisor
Peter Marais
Posts: 78
Registered: ‎08-20-2003
Message 1 of 5 (502 Views)
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max luns/hba

What is the maximum luns per fibre channel hba supported on Tru64 v5.1B-4. According to the scsi-3 technical specs it is 256/hba. Is this true as I have a customer running a lot more than that.
Frequent Advisor
DCBrown
Posts: 51
Registered: ‎01-16-2007
Message 2 of 5 (502 Views)

Re: max luns/hba

The maximums for V5.1B are:

Up to 255 HBAs (could be separate fabrics),
Up to 255 controllers per HBA (nports),
Up to 255 LUNs per controller.

So for each hba, the maximum luns is therefore 65,025.

BTW, the lun range is 0..254. Lun 255 is assigned to an internal layer within the kernel (xpt) if memory serves.

The bus/target/lun nomenclature used within the system refers to hba, controller (nport), and lun behind that controller respectively.

Hope that helps.
Bud

Frequent Advisor
Peter Marais
Posts: 78
Registered: ‎08-20-2003
Message 3 of 5 (502 Views)

Re: max luns/hba

Thanks Bud

But unclear to me. Does HBA not mean host bus adapter which in that case means controller.

Thus to my knowledge the hba plugs into the pci backplane and according to the documentation can only handle 256 LUN's (scsi-3 standard)Please try and explain in more detail.
Frequent Advisor
DCBrown
Posts: 51
Registered: ‎01-16-2007
Message 4 of 5 (502 Views)

Re: max luns/hba

HBA is host bus adapter. My reference to controller is shorthand for storage controller.

The scsi standard refers to at most 256 LUNs per target, where the target is a particular controller port for SANs.

So the HBA can send commands to any one of 255 different storage controllers that it can see and has logged into out on the SAN, and behind each of those storage controllers up to 255 LUNs can be addressed. This is one less than the standard because the kernel uses one of the LUNs internally.

Although the scsi command has which LUN the command is addressed to, the FC-SCSI protocol determines how that scsi command is routed to the target storage controller. This routing is controlled by information outside of the scsi command itself. Only after the command arrives within the storage controller is LUN really relavant.

Bud
Frequent Advisor
Peter Marais
Posts: 78
Registered: ‎08-20-2003
Message 5 of 5 (502 Views)

Re: max luns/hba

Thanks Bud, got it now
max luns/hba=max nports/hba x max luns/nport
= 255 x 255=65025
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