Summary: How are SCSI target ids decided ?

From: TAG DBA <>
Date: Wed Jul 11 2001 - 01:06:29 EDT
Pls excuse the delay in sending out the summary for my query. I wanted =
to actually wait and see what SCSI target ids were given when we had =
popped in our disks in our E450. This was done day before yesterday.
I got a number of responeses - and I thank all of those who wrote back.
Thanks to :
Petri Kallberg ,Valeriy Glinskiy ,Cagri Yucel ,Harrington, David =
B,Franczyk Gerald,gabriel rosenkoetter ,Herpers, Joseph=20
Petri was also kind enough to clarify my further queries offline.
My original mail is posted below the summary.

----------------Summary Starts---------------------------

A disk device is commonly refereed to as c[X]t[X]d[X]s[X]
In reverse order
sX - stands for slice (ranging ffrom 0 to 7 for Sun on Sparc)
dX - I believe refers to some logical disk number - its 0 for SCSI disks
tX - is what I was trying to figure out
cX -refers to controller or channel - the term is used a little losely.=20

My question was - how were SCSI target ids decided on the E450. This is =
how a disk bay looks like on a Sun E450
The numbers along side are what I shall refer to as disk numbers on the =
storage bay in this email
	10 =3D=3D=3D=3D	|   =3D=3D=3D=3D=3D=3D 11
	8 =3D=3D=3D=3D=3D	|   =3D=3D=3D=3D=3D=3D 9=20
	6 =3D=3D=3D=3D=3D	|   =3D=3D=3D=3D=3D=3D 7	(this is an add on bay for 8 =
	4 =3D=3D=3D=3D=3D	|   =3D=3D=3D=3D=3D=3D 5
	2 =3D=3D=3D=3D=3D	|   =3D=3D=3D=3D=3D=3D 3	(this bay takes 4 disks)
	0 =3D=3D=3D=3D=3D	|   =3D=3D=3D=3D=3D=3D 1

I was trying to figure out controller association and target ids =
allocation if disks were mounted in all the above slots.
This is how it is :

Controller		Target Id				SCSI Target ID	=09
Con-2, Chn-1	c3-t2	10 =3D=3D=3D=3D  |   =3D=3D=3D=3D=3D 11	c3-t3
Con-2, Chn-1	c3-t0	8 =3D=3D=3D=3D=3D  |   =3D=3D=3D=3D=3D 9 	c3-t1
Con-2, Chn-0	c2-t2	6 =3D=3D=3D=3D=3D  |   =3D=3D=3D=3D=3D 7	c2-t3
Con-2, Chn-0	c2-t0	4 =3D=3D=3D=3D=3D  |   =3D=3D=3D=3D=3D 5	c2-t1
Con-1, Chn-0	c0-t2	2 =3D=3D=3D=3D=3D  |   =3D=3D=3D=3D=3D 3	c0-t3
Con-1, Chn-0	c0-t0	0 =3D=3D=3D=3D=3D  |   =3D=3D=3D=3D=3D 1 	c0-t1

Channel 1 on controller 1 is used for tape and CD-ROM device.
I tested this out when we set up our E450 and that was how it worked =
----------------Summary Ends---------------------------

Other emails that I got have been reproduced below.
Unfortunately, the E450s scsi controllers are pretty much independant =
the drive bays...=20
This is because:

Controller numbers are designated at the time of install.
They come with some soft cables that can be attached to any of the drive
The drive bay backplanes can be added one at a time.

Therefore, you might add the backplanes for 4 disks one day (and it will =
named c1)
Add a couple of controller cards for tape backups the next day (named =
c2, c3
and c4)
And then add another set of backplanes for another 4 disks the day after
that (and it would wind up being named c5)

The quickest way to determine which disk is which when it comes to an =
is the brute force method.
You can run the "format" command, choose the "analyze" menu and then =
the "test" option.
If the system is fairly quiet, the light on the disk drive will then =
differently from the others.

This way, you can verify which controllers and which channels go where.

Gary Franczyk
System Administrator
Motorola, Inc.
> an other suggests that we pop in each disk and reconfigure the machine
> and see what scsi target id is being given !!!

I'm with that guy. You won't break anything by doing so (don't go
hot swapping or switch the machine off without shutting down
properly, of course), and you'll be sure since you mapped it out
yourself. (If these are your only disks, you'll want to be booting
off a CD while you're moving things around.)
        ~ g r
c0t0d0s0 describes your hard disk:

c0	Logical Controller Number
t0	Physical Bus Target ID
d0	Drive Number
s0	Slice (a slice under Solaris is like a partition under

I have attached 2 gifs from our software that may clarify some of your
questions. I have more info if you need it.

Joe Herpers
The device name cCtTdDsS is made so that

	C =3D SCSI controller ID
	    (note that 1 PCI card can multiple controllers)
	T =3D SCSI target ID. Targets are unique within controller
	    (c0t0... and c1t0 have both ID 0 but different controllers)
	D =3D SCSI device ID. This is typically set to 0 (in your case anyway)
	S =3D Disk slice. One disk can be partitioned upto 7 slices.
	    (0-7, but slice 2 is reserved for whole disk)

SCSI target ID for your disk depends where you have installed it. SCSI =
on E450 assigns IDs for disks. Disk bays are grouped into groups of 4. =
from bottom the first 4 slots are numbered as follows

		ID 2	!	ID 3
		ID 0	!	ID 1	   =20
This is always controller 0 (c0), the rest of the bays depend how you =
installed you pci cards and connected cables. Anyway, the same grouping =
4 disk and target ids applies.

No. IDs are unique within controller. By controller I mean here a =
1 PCI card has 2 channels -> ONLY IDs 0-3 are used.=20

Numbering goes propably like this

			c3t2	c3t3
			c3t0	c3t1

			c2t2	c2t3
			c2t0	c2t1
			c0t2	c0t3
			c0t0	c0t1
(c2 and c3 could also be otherway depending on your cables)

Note that c1 is is missing from the picture. It is used for internal
devices (tape, cdrom) and backpanel scsi-interface. Hope this helps ...

Petri Kallberg
Sun Microsystems Oy

"c" stands for "controller". Here is the link to the article which =
help you to find the answer
Valeriy Glinskiy []
Here is what I did, as your main purpose is to distribute disks equally
among controllers, simply open the disk door of 450 and insert disks
equally distributed to the slots. Considering you have 6 disks, use
slots 0,1,4,5,8,9. That is done. At the Ok prompt using probe-scsi-all,
you may check the situation using above controller codes.

Hope this helps.
It's Controller, Target, Drive, Slice (c0t0d0s0).

The format command will let a root user read the setup; selection 0 is
c0t0d0, p,p will let you view the slices. Selection 1 would probably be
c0t1d0, but, on other machines it may be c1t0d0.

read the man pages on format for more info.

Dave Harrington

And finally my original question :

Hello SunManagers,
I am a DBA who is overlooking installation and setup of a brand new E450
server. I wanted to decide on my disk=20
partitions and wanted to know what scsi target ids would be allocated to =
6 disks in the server. The
installation manual says that target ids are pre-decided (starting from =
onwards) on the back-plane for
the disk bay. I had a few queries - to which my system admins havent =
able to answer (I have already gone thru
5-6 books on Sun Solaris and the Manuals. Hence posting this email.)
Please confirm if my understanding is right :

rol-			SCSI
ler	Channel	ID	Device	Disk Name
0	1			CD ROM	-
	1			Tape Drive	-
(other 2 channels for 2 external SCSI devices)
0	2		0	Disk0		c0t0d0
	2		1	Disk1		c0t1d0
	2		2	(BlankBay)	c0t2d0
	2		3	(BlankBay)	c0t3d0
1	1		0	Disk2		c1t0d0
	1		1	Disk3		c1t1d0
	1		2	(BlankBay)	c1t2d0
	1		3	(BlankBay)	c1t3d0
1	2		4	Disk4		c1t4d0
	2		5	Disk5		c1t5d0
	2		6	-		c1t6d0
	2		7	-		c1t7d0

I not using 2 disk bays on Controller 0 - Channel 2 , because I want to
utilise the otherwise
unused Controller 1 - Channel 2 (an attempt to distribute i/o)
Now I am confused whether I have got the SCSI id column correct ? The =
logical name will depend on my
SCSI ID and thats where I am stuck.
One of my sys-admin says that C (in cXtXdXsX) stands for "controller", =
other says it stands for "channel" and an=20
other suggests that we pop in each disk and reconfigure the machine and =
what scsi target id is being
given !!!
So what I want to know is how are target ID's given ? Are target ids =
for a combination of "controller+channel"
or are they unique only for a controller.=20
Other details : SunE450 sun4u=20
Thanks and Regards,
Received on Wed Jul 11 06:06:29 2001

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