Scsi and Fibre channel

[SAM_24]

Hi,

I was told hp-ux sees fibre channel device as scsi device. Is it correct? I am having hard time understanding it. HBA driver presents FC device as scsi device? Is it correct regardless of whether the disk is scsi or FC, system still uses /dev/dsk/cNtNDN nameing convention? What is the maximum number of devices can be connected on particular FC target?

[Kent Ostby]

I can only answer part of your question, but yes you will use the /dev/dsk/cNtNDN convention for SCSI or Fibre disks.

[Jeff Schussele]

Hi,

You can have up to 16 targets (cXt0-15dZ) & 8 LUNs (cXtYd0-7)per target so you you can have up to 128 devices per controller, I believe.

Rgds,
Jeff

[Bharat Katkar · Accepted solution]

Hi there,
I would like to add something to it.
Fibre Channel is devided into 4 layer just like TCP/ip.

The upper layer protocol of Fibre Channel i.e. FC4 does the this Job. FC4 layer protocol coverts SCSI commands into Fibre Channel protocol and vice versa. Mapping of disk device to device files is also done at this layer and you finally see that cxtxdx device as usual.

Regards,
Bharat

[Uwe Zessin]

Fibre Channel uses five(5) layers:
FC-4 - mapping layer
FC-3 - common services
FC-2 - framing protocol layer
FC-1 - encoding/decoding layer
FC-0 - physical layer

Serial SCSI protocol is mapped into FC-4. It can be a bit confusing that this mapping is called "FCP" (Fibre Channel Protocol), but it just means 'running serial SCSI protocol over a Fibre Channel infrastructure'.

The maximum number of LUNs that can be addressed behind a target depends on the addressing mode and the mapping of FC LUNs to the operating system's I/O structure.

Many storage systems can present way more than 8 LUNs per storage controller port. HP-UX will create additional 'pseudo-targets' to be able to address more than just 8 LUNs.

[Bharat Katkar]

Uwe when i was reading fc3 was under construction and functionally not present. This theorotically in the book. Don't know whether common services are in plase right now. That's why i skipped that one.

[RAJESH GANGADHARAN]

Hi,

You can have up to 16 targets (cXt0-15dZ) & 8 LUNs (cXtYd0-7)per target so you you can have up to 128 devices per controller, I believe.

Rgds,
Jeff

Let me add some more to Jeff's input, if you are using XP array you can have maximun of 255 (FF) Luns attahched to one HBA. here the naming convention will be from cXt0d0 to cXt15d15 (for example let's take example c10t15d7), next lun address will be start with a different controller instance number
i.e c(X+1)t0d0 to c(X+1)t15d7 (using the same example the next device file will be c11t0d0 and it will continue till c11t15d7). It is not mandatory that the next controller instance will be X+1.

[Uwe Zessin]

Hello Bharat,
that is what I got told some years ago, too.

I have seen some descriptions the other day and they have associated functions like the name server, the time server and so on with the FC-3 layer.