Re: Mount by WWN (FC, using qlogic 2200)

On Wed, 2004-02-04 at 18:12, Bryan Henderson wrote:

But it doesn't identify the "device" as Linux defines a device.  Setting
aside multiple paths for the moment, a Linux sd device corresponds to an
FCP logical unit, and the WWN identifies an FCP target (aka physical unit).
I.e. where a physical unit has multiple logical units, multiple linux sd
devices can have the same WWN.

Actually, the SPC-3 (rev 16) section 7.6.4.1 does say the Device
Identification VPD Page ... [shall apply] to the logical unit.

Of course, not all devices obey this, as you say, but still.

James

On Wed, 2004-02-04 at 18:12, Bryan Henderson wrote:

quoted

But it doesn't identify the "device" as Linux defines a device. 

Setting

quoted

aside multiple paths for the moment, a Linux sd device corresponds to 

an

quoted

FCP logical unit, and the WWN identifies an FCP target (aka physical 

unit).

quoted

I.e. where a physical unit has multiple logical units, multiple linux 

sd

quoted

devices can have the same WWN.

Actually, the SPC-3 (rev 16) section 7.6.4.1 does say the Device
Identification VPD Page ... [shall apply] to the logical unit.

Of course, not all devices obey this, as you say, but still.

I stand corrected.  Upon further investigation, I realize that I confused 
WWN with WWNN.  WWN (worldwide name) is a generic term referring to, well, 
world wide names.  There are at least 3 WWNs in FCP systems:  WWPN 
(worldwide port name) to identify a port in an FC network, WWNN (worldwide 
node name) to identify a node in an FC network, which corresponds to an 
FCP target (physical unit), and a logical unit WWN, which I have seen 
called LUSN (Logical Unit Serial Number), but now I see others calling it 
the LU WWN and logical unit name too.

I haven't see any relevant standards, but I'll take your word for it that 
SPC-3 calls the VPD field in question a 'WWN' and because it's a VPD page 
for a logical, that means it is the LU WWN.

On Wed, 2004-02-04 at 19:33, Bryan Henderson wrote:

I stand corrected.  Upon further investigation, I realize that I confused 
WWN with WWNN.  WWN (worldwide name) is a generic term referring to, well, 
world wide names.  There are at least 3 WWNs in FCP systems:  WWPN 
(worldwide port name) to identify a port in an FC network, WWNN (worldwide 
node name) to identify a node in an FC network, which corresponds to an 
FCP target (physical unit), and a logical unit WWN, which I have seen 
called LUSN (Logical Unit Serial Number), but now I see others calling it 
the LU WWN and logical unit name too.

I haven't see any relevant standards, but I'll take your word for it that 
SPC-3 calls the VPD field in question a 'WWN' and because it's a VPD page 
for a logical, that means it is the LU WWN.

Each identifier on the SPC-3 Device Identification VPD page (page 83)
has an "association" field, with one of the following values:

- The IDENTIFIER field is associated with the addressed logical unit. 
- The IDENTIFIER field is associated with the SCSI target port that
received the request. 
- The IDENTIFIER field is associated with the SCSI target device that
contains the addressed logical unit. 

So, an identifier on page 83 may be either an LU WWN, WWPN, or a WWNN. 

We need to check the association field, and use the identifier
appropriately, and we need to insist that storage vendors implement it
correctly.

On Thu, 2004-02-05 at 08:56, Tom Coughlan wrote:

Each identifier on the SPC-3 Device Identification VPD page (page 83)
has an "association" field, with one of the following values:

- The IDENTIFIER field is associated with the addressed logical unit. 
- The IDENTIFIER field is associated with the SCSI target port that
received the request. 
- The IDENTIFIER field is associated with the SCSI target device that
contains the addressed logical unit. 

So, an identifier on page 83 may be either an LU WWN, WWPN, or a WWNN. 

Actually, this isn't an either/or, the page may contain a list. 
However, the standard is very clear (7.6.4.11.3) that each LUN that is
not a well known LUN shall have at least one identifier of association 0
(Logical Unit Identifier).

We need to check the association field, and use the identifier
appropriately, and we need to insist that storage vendors implement it
correctly.

I agree, but I see this as a userspace issue.

James