I always thought c=controller, t=target, d=disk, s=slice.
How exactly are they assigned? My internal drive is c0t1d0. But if I connect an external box, it jumps to c2t10d0, c2t11d0 etc. Is t=target? What exactly does those t-numbers mean and why does it jump to t10, t11 instead of going sequentially?

The system points to an external target id differently. It is auto assigned by the system. Nothing wrong with the "jump" in the target number you see.

Oh...so the controller and the target are not related at all? I was told that t0 or t1 is something like a split cable (that you typically see in a desktop.. cable that connects HDD and/or cdrom or floppy drive) which are target0 and target1. Is it wrong?

It depends on the hardware itself. Some machines you will see it starts with c2t0d0 and c2t1d0...it really depends on the hardware itself. You can check the hardware documentation of your machine and you will see how things are organized.

Yes, you should tell what kind of disks these are (SCSI, SAS, USB or whatever).

Two internal drives are fiber channel and the storage box has SCSI drives...Thanks for the help, all of you!!