I'm trying to install a new drive in a server. It's a Seagate SCSI drive.

Running sg_map shows that it has been detected at:

/dev/sg3 but it is not mapped to anything.

I need to map it to say: /dev/sdd

Then I know I need to run fdisk to partition it and mk2efs -j to create the file system then mount it.

So how do I map /dev/sg3 to /dev/sdd ?

Maybe I have got the wrong end of the stick but....
If the drive is detected at /dev/sg3 then you should be able to run fdisk like this:

#fdisk /dev/sg3

and then you can

#mk2efs -j /dev/sg3

then mount it.

If you also want to refer to it as /dev/sdd then perhaps you chould make a link?

Hope this helps

When I type fdisk /dev/sg3 nothing appears to happen, should it prompt me? it just seems to hang.

You say "When I type fdisk /dev/sg3 nothing appears to happen,"

Well, something should happen. When I try that command, fdisk says "Unable to open /dev/sg3", which is not surprising as I do not have a /dev/sg3 (That strikes me as a weird device number anyway).

Let's start at the beginning.
You have installed a new SCSI drive. Did you set it's SCSI ID number correctly? Is the SCSI Bus terminated correctly? Does your SCSI controller "see" your new disk?

What SCSI controller are you using? If it's a Adaptec, there's usually something you can press at power-on to set up the controller ( a bit like the procedure to set up your PS's BIOS ) and make sure that it is scanning the SCSI bus for, and is seeing your new disk.

When I ran a SCSI unix system (years ago I admit), the SCSI disks appeared as /dev/sda /dev/sdb etc. Their partitons were then referred to as /dev/sda1 /dev/sda2 etc. "sg3" is weird.

I am unfamiliar with Debian, and do not know anything about sg_map.

SG_MAP shows this: /dev/sg3 is the 3rd, newest, drive to be installed

nnco2:/var/log# sg_map
/dev/sg0 /dev/sda
/dev/sg1 /dev/sdb
/dev/sg2 /dev/sdc
/dev/sg3

SG_SCAN shows this:

nnco2:/var/log# sg_scan
/dev/sg0: scsi0 channel=0 id=0 lun=0 type=0
/dev/sg1: scsi0 channel=0 id=1 lun=0 type=0
/dev/sg2: scsi0 channel=0 id=2 lun=0 type=0
/dev/sg3: scsi0 channel=0 id=8 lun=0 type=3

Is the id number wrong? If so how do I change this? Its in an IBM eServer so I just mounted it in the tray and put it in.

If I type fdisk /dev/sdd I get unable to open /dev/sdd which makes sense.

Ok:
1] I have no idea what an "IBM eServer" is, but it probably doesn't matter. Is it a mainframe or desktop PC?
2] I still do not understand this sg business, but your "sg_map" and "sg_scan" appear to show that the latest device is:

/dev/sg3: scsi0 channel=0 id=8 lun=0 type=3

It's SCSI ID is 8, which may be OK as it is different from the other disks IDs, but some SCSI controllers only support 8 devices: it might be an idea to set this disk's SCSI ID to 3 (sort of logical if you look at how the other disks have been allocated SCSI IDs). You usually do this on the disk itself: there will be jumpers for you to set the ID number in a binary fashion: Check your disk's documentation - it should tell you, or get its model number and search seagate (or google).

The other thing that is worrying is that sg_scan shows your new disk to be of "type=3", whereas all the other disks are type=0. I cannot do "man sg_scan", as I do not have this utility, but you could. Find out what it means by "type".

fdisk -l (that's a lower case L) may give you some useful information on what is where.

PS what filesystem are you using? If it is RAID, then I am WAY out of my depth here.
Sorry to be slow replying, I have a real job as well
Hope this helps.