Disk Device File Specifications

[Scott J. Showalter]

Our Storage Team has posed the following question:

What are the ranges of numbers that can be used to make up the minor number of a device file? To be more specific, they want to know if the D portion of the number can exceed 7? e.g.
brw-r----- 1 bin sys 31 0x37f700 Sep 3 2003 c55t15d7

I know that the name c55t15d7 is just a name, and that it can be anything. In this example c55 represents 55dec=37hex, 15dec=Fhex, and 7dec=7hex in the minor number.

So the real question is: Can the 3rd to the last position in the minor number be greater than 7?

[Patrick Wallek]

Nope, not that I know of. Once you hit c?t?d7, then the next device file is c?t?+1d0.

[Geoff Wild · Accepted solution]

Yes - see man insf:

Many special files are named using the ccardttargetddevice naming
convention. These variables have the following meaning wherever they
are used.

card The unique interface card identification number from
ioscan (see ioscan(1M)). It is represented as a
decimal number with a typical range of 0 to 255.

target The device target number, for example the address on a
HP-FL or SCSI bus. It is represented as a decimal
number with a typical range of 0 to 15.

device A address unit within a device, for example, the unit
in a HP-FL device or the LUN in a SCSI device. It is
represented as a decimal number with a typical range of
0 to 15.


Rgds...Geoff

[Naveej.K.A]

hi,

c- controller instance number defined by /etc/ioconfig
t- target or scsi id for the device
d- for the lun only used in raid arrays

regds
Naveej

[Patrick Wallek]

OK, I saw Geoffs post for insf, HOWEVER I have never had a 'd' number go beyond 7. Mine always behave in the manner I indicated in my first response.

[Scott J. Showalter]

OK, now they are telling me they know that HP-UX supports numbers greater than 7, but they need to know if EMC Symetrix supports the number greater than 7.

They can't find out the information from EMC, so asked me to see if I can find out through HP.

[Sridhar Bhaskarla]

I am really surprized to see the man page as provided by Geoff.

My understanding is that the limit is 8 LUNs per target. EMC does have the capability to address more than that number, I am sure. But still HP will translate it to tx+1d0 if it is more than 8 LUNs.

-Sri

[Jeff Schussele]

Hi,

You'll never see d>7 even on true Wide SCSI disk connections. In those cases the SCSI ID will = target. And you'll certainly never see them on SCSI -to-> FC LUN translations. Above answers are correct. As I understand it the true limits are in decimal:

0 <= c =< 255
0 <= t =< 15
0 <= d =< 15

But for disk devices it's:

0 <= d =< 7

The Target+1 for LUN > 7 is a legacy deal when the OS wouldn't support but 128 total devices per HBA I believe. And it's just kind of hung on ever since.

So the answer is yes AND no. Yes - HP supports d > 7, but NO they don't for disk devices. I *think* they do for tape library devices - but I'm not positive.

Rgds,
Jeff

[Patrick Wallek]

Whether or not the EMC supports the 'd' portion of c?t?d? is a pointless question. The EMC doesn't care about those device files. It will present a LUN for your HP-UX machine to access. The HP-UX machine will associate the hardware path of the EMC LUN (something similar to 0/7/0/0.1.16.0.0.1.0 -- This is actually LUN 8 on a VA7400)and will associate the device file (mine is c12t1d0 in this case) with it.

[Jeff Schussele]

Well summed up Patrick.
Just another of those cases where HP says......Never mind what we *say* - you'll do it as we want.
No big whoop - just need to know the enforced rules.

Rgds,
Jeff

[Scott J. Showalter]

Patrick,

Our storage team has the ability to present the LUN to us in a number of different ways. They are asking this question because they can control the hardware path that is presented to the server.