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".
(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.